Story highlights Safety of international experts at the scene must be ensured, Vladimir Putin says

Ukrainian Cabinet says teams have found 251 bodies at the crash site so far

OSCE observers don't know whether black boxes were found, spokesman says

Rebel leader tells ABC: "We can and we want to give bodies to the relatives"

Are the same separatists accused of shooting down Malaysia Airlines Flight 17 now looting, tampering with the evidence and stopping investigators from combing through the wreckage?

Three days after the passenger plane plunged to the ground, criticism over the handling of the crash site in rebel-controlled eastern Ukraine showed no signs of slowing on Sunday.

Key questions remain unanswered: What will happen to the remains of the 298 people aboard the plane that crashed Thursday? Where are the black boxes? And is there any hope investigators will be able to determine who's responsible?

Malaysia's transportation minister said an international team was "effectively being prevented from entering the crash site," adding in a statement that officials were concerned that "the sanctity of the crash site has been severely compromised."

In an interview with CNN's Candy Crowley, Secretary of State John Kerry described what he said were "drunken separatists piling the remains of people into trucks in an unceremonious fashion ... interfering with the evidence in the location."

He told NBC's "Meet the Press" that there is a "buildup of extraordinary circumstantial evidence" over the crash that Russia "needs to help account for."

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And British Prime Minister David Cameron didn't mince words when he said who was to blame. In an op-ed in The Sunday Times, he called the plane crash and its aftermath "an outrage made in Moscow."

Russian President Vladimir Putin fired back with a video statement posted on the Kremlin's official website early Monday, arguing that his country has been pushing for peace in Ukraine.

"We have repeatedly called on all parties to immediately stop the bloodshed and to sit down at the negotiating table. We can confidently say that if June 28 fighting in eastern Ukraine did not resume, this tragedy most likely would not have happened," he said. "However, no one should have the right to use this tragedy to achieve selfish political objectives. Such events should not divide but unite people."

He stressed that safety must be guaranteed for international experts investigating the crash.

"We must do everything to ensure their work has full and absolute security (and) ensure necessary humanitarian corridors are provided," Putin said.

At the crash site, there were concerns the bodies had been picked over by thieves.

"The facts of looting, how the terrorists are dealing with the bodies, are beyond the moral boundaries," Ukrainian President Petro Poroshenko tweeted.

The local head of the rebels rejected accusations that his forces shot down the plane, denied accusations that they removed the bodies and denied responsibility when asked about people reportedly using stolen bank-issued cards taken from the victims' bodies.

"It is possible that some local residents could have searched the bodies of victims, found their cards and tried to use them. Unfortunately, I can't exclude the possibility of this," Alexander Borodai said Saturday.

Nearly 200 bodies kept in refrigerated train cars

The situation at the crash site showed some small signs of improvement on Sunday, with more control and more activity.

"Today was a better day for sure," said Michael Bociurkiw, a spokesman for the Organization for Security and Co-operation in Europe's monitoring team in Ukraine. "We were able to spend quite a bit of time out at the different crash sites."

But it was still far from a well-organized investigation scene, and the area remained under the control of pro-Russia rebels.

Government emergency workers prevented vehicles from driving up the road to the main crash site, but people could still roam the fields on foot.

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Photos: Photos: Reaction to MH17 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – Families of crew members aboard Malaysia Airlines Flight 17 gather for a vigil Tuesday, July 22, in Kuala Lumpur, Malaysia. All 298 people aboard the passenger plane died when it was shot down Thursday, July 17, in a rebel-controlled part of eastern Ukraine. Hide Caption 1 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – A woman cries July 22 during a service near the crash site. Hide Caption 2 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – People in Melbourne gather to mourn the victims during a candlelight vigil at Federation Square on July 22. Hide Caption 3 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – In memory of two Newcastle United fans who died in the crash, two wreaths are placed on seats July 22 at the Forsyth Barr Stadium in Dunedin, New Zealand. The soccer fans were traveling to New Zealand to watch their team play in a preseason tournament. Hide Caption 4 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – A KLM employee reaches out into a sea of flowers July 22 at Schiphol Airport in Amsterdam, Netherlands. Hide Caption 5 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – A flower and stuffed animal sit near the crash site on Monday, July 21. Hide Caption 6 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – A woman in Kuala Lumpur attends a candlelight vigil on July 21. Hide Caption 7 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – Ukrainian President Petro Poroshenko attends a flower-laying ceremony at the Dutch Embassy in Kiev, Ukraine, on July 21. Although the passengers came from all over the world, many of them were Dutch because the flight originated in Amsterdam. Hide Caption 8 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – A woman places a flower during a candlelight vigil in Kuala Lumpur on July 21. Hide Caption 9 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – Mourners in Eynesbury, Australia, attend a memorial service Sunday, July 20, for a family of five killed in the disaster. Hide Caption 10 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – Buddhist monks in the Malaysian capital light candles during a special prayer for the victims on July 20. Hide Caption 11 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – Wildflowers lie on an engine from the crashed jet on Saturday, July 19. Hide Caption 12 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – Friends of Nur Shazana Mohamed, a crew member aboard the flight, take part in a special remembrance prayer at a mosque in Putrajaya, Malaysia, on July 19. Hide Caption 13 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – Dutch Prime Minister Mark Rutte signs a condolence register at the Ministry of Safety and Justice in The Hague, Netherlands, on Friday, July 18. "I want to see results in the form of unimpeded access and rapid recovery," Rutte said in a press briefing. "This is now priority number one." Hide Caption 14 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – People pray for the victims of Malaysia Airlines Flight 17 at a church outside Kuala Lumpur on July 18. Hide Caption 15 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – A woman in Berlin places a candle at a memorial on July 18. Hide Caption 16 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – People in Kiev gather to mourn the victims on July 18. Hide Caption 17 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – Akmar Binti Mohd Noor, whose sister was aboard Flight 17, cries outside the family holding area at Kuala Lumpur International Airport on July 18. Hide Caption 18 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – A man prays at a memorial in front of the Dutch Embassy in Kiev on July 18. Hide Caption 19 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – Dutch cyclists wear a black armband in honor of the crash victims during the 13th stage of the Tour de France on July 18. Hide Caption 20 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – Dutch Justice Minister Ivo Opstelten observes a moment of silence after signing a condolence book in The Hague on July 18. Hide Caption 21 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – Candlelight prayers honor the victims at a church outside Kuala Lumpur on July 18. Hide Caption 22 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – Floral tributes adorn the entrance to Schiphol Airport in Amsterdam. Hide Caption 23 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – A Dutch flag flies at half-staff in The Hague on July 18. Hide Caption 24 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – People place flowers in front of the Dutch Embassy in Moscow on July 18. Hide Caption 25 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – Students attend a prayer July 18 in Central Java, Indonesia. Their teacher John Paulissen was a passenger on Flight 17. Hide Caption 26 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – Russian President Vladimir Putin, center, and members of his government observe a moment of silence on Thursday, July 17. Hide Caption 27 of 28 Photos: Photos: Reaction to MH17 World reacts to MH17 crash – People pay tribute to the victims outside the Dutch Embassy in Kiev on July 17. Hide Caption 28 of 28

Search teams have found 251 bodies at the crash site, the Ukrainian Cabinet said on its website.

Pro-Russian rebels are keeping the remains of nearly 200 MH17 victims in refrigerated train cars, Vice Prime Minister Volodymyr Groysman said Sunday, adding that talks were ongoing for their release.

OSCE observers went to a train station about 15 kilometers (9 miles) from the main crash site to see the bodies, Bociurkiw said.

"We were able to peer inside of the cars, and it definitely was refrigerated. There was no way we could verify the count of ... bodies, but there were dozens and dozens there," he told CNN. "We were told those railway cars will remain stationary until international experts arrive."

Earlier Sunday, Russian state news agency RIA Novosti reported that the train was headed to Donetsk.

Borodai told ABC News on Sunday that rebels want to release the remains.

"We can and we want to give bodies to the relatives, but experts have to examine the bodies here. That is international practice," Borodai told ABC.

If the remains are turned over to the Ukrainian government, Borodai said he feared that they would be used as evidence to blame his fighters for shooting down the plane -- an accusation he has repeatedly denied.

He said he guaranteed the safety of international investigators "and their ability to work."

But Ukraine's State Emergency Service said the search in the remote area of eastern Ukraine, roughly 25 miles (40 kilometers) from the Russian border, was being "complicated by armed separatists at the site who hinder the work of SES units."

Hundreds of staffers from the agency are searching for the remains of the MH17 victims, covering an area stretching across 13 square miles (34 square kilometers).

Busloads of volunteers from nearby coal mines also fanned out across the wheat fields where the bodies and debris from the plane fell.

Malaysia is sending two large military cargo planes to bring back the remains, the country's official news agency Bernama reported.

Black boxes found?

Pro-Russia rebels may have recovered the plane's flight data and cockpit voice recorders, Borodai said on the website of the self-declared Donetsk People's Republic.

If experts determine the devices found are the so-called black boxes, they will be turned over to international investigators, Borodai said.

"These are some technical objects. We cannot say for sure these are black boxes," he said.

Borodai said the devices are under guard in the region. They will not be given to Ukrainian officials, he said.

Reuters distributed video on Sunday of what appeared to be an inflight recorder found by a worker in a field. The agency labeled the video, shot Friday, as showing one of the two flight data recorders from MH17.

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Photos: Malaysia Airlines Flight 17 crashes in Ukraine Photos: Malaysia Airlines Flight 17 crashes in Ukraine Debris from Malaysia Airlines Flight 17 sits in a field at the crash site in Hrabove, Ukraine, on September 9, 2014. The Boeing 777 was shot down July 17, 2014, over Ukrainian territory controlled by pro-Russian separatists. All 298 people on board were killed. In an October 2015 report, Dutch investigators found the flight was shot down by a warhead that fit a Buk rocket, referring to Russian technology, Dutch Safety Board Chairman Tjibbe Joustra said. Hide Caption 1 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine Australian and Dutch experts examine the area of the crash on August 3, 2014. Hide Caption 2 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine A woman walks with her bicycle near the crash site on August 2, 2014. Hide Caption 3 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine Police secure a refrigerated train loaded with bodies of passengers from Malaysia Airlines Flight 17 as it arrives in a Kharkiv, Ukraine, factory on July 22, 2014. Hide Caption 4 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine A pro-Russian rebel passes wreckage from the crashed jet near Hrabove on Monday, July 21, 2014. Hide Caption 5 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine – Wreckage from the jet lies in grass near Hrabove on July 21, 2014. Hide Caption 6 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine A man covers his face with a rag as members of the Organization for Security and Co-operation in Europe and the Dutch National Forensic Investigations Team inspect bodies in a refrigerated train near the crash site in eastern Ukraine on July 21, 2014. Hide Caption 7 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine Emergency workers carry a victim's body in a bag at the crash site on July 21, 2014. Hide Caption 8 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine A piece of the plane lies in the grass in eastern Ukraine's Donetsk region on July 21, 2014. Hide Caption 9 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine An armed pro-Russian rebel stands guard next to a refrigerated train loaded with bodies in Torez, Ukraine, on Sunday, July 20, 2014. Hide Caption 10 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine Ukrainian State Emergency Service employees sort through debris on July 20, 2014, as they work to locate the deceased. Hide Caption 11 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine A woman covers her mouth with a piece of fabric July 20, 2014, to ward off smells from railway cars that reportedly contained passengers' bodies. Hide Caption 12 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine Toys and flowers sit on the charred fuselage of the jet as a memorial on July 20, 2014. Hide Caption 13 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine People search a wheat field for remains in the area of the crash site on July 20, 2014. Hide Caption 14 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine A woman walks among charred debris at the crash site on July 20, 2014. Hide Caption 15 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine Emergency workers load the body of a victim onto a truck at the crash site on Saturday, July 19, 2014. Hide Caption 16 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine Emergency workers carry the body of a victim at the crash site on July 19, 2014. Hide Caption 17 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine A large piece of the main cabin is under guard at the crash site on July 19, 2014. Hide Caption 18 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine Victims' bodies are placed by the side of the road on July 19, 2014, as recovery efforts continue at the crash site. International officials lament the lack of a secured perimeter. Hide Caption 19 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine A man looks through the debris at the crash site on July 19, 2014. Hide Caption 20 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine An envelope bearing the Malaysia Airlines logo is seen at the crash site on July 19, 2014. Hide Caption 21 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine Armed rebels walk past large pieces of the Boeing 777 on July 19, 2014. Hide Caption 22 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine Ukrainian rescue workers walk through a wheat field with a stretcher as they collect the bodies of victims on July 19, 2014. Hide Caption 23 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine A woman looks at wreckage on July 19, 2014. Hide Caption 24 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine Pro-Russian rebels stand guard as the Organization for Security and Co-operation in Europe delegation arrives at the crash site on Friday, July 18, 2014. Hide Caption 25 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine A woman walks through the debris field on July 18, 2014. Hide Caption 26 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine Pro-Russian rebels stand guard at the crash site. Hide Caption 27 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine Wreckage from Flight 17 lies in a field in Shaktarsk, Ukraine, on July 18, 2014. Hide Caption 28 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine A man covers a body with a plastic sheet near the crash site on July 18, 2014. The passengers and crew hailed from all over the world, including Australia, Indonesia, Malaysia, Germany and Canada. Hide Caption 29 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine A diver searches for the jet's flight data recorders on July 18, 2014. Hide Caption 30 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine Coal miners search the crash site. Hide Caption 31 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine Wreckage from the Boeing 777 lies on the ground July 18, 2014. Hide Caption 32 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine People search for bodies of passengers on July 18, 2014. Hide Caption 33 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine A woman walks past a body covered with a plastic sheet near the crash site July 18, 2014. Hide Caption 34 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine Belongings of passengers lie in the grass on July 18, 2014. Hide Caption 35 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine People inspect the crash site on Thursday, July 17, 2014. Hide Caption 36 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine People walk amid the debris at the site of the crash. Hide Caption 37 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine Debris smoulders in a field near the Russian border. Hide Caption 38 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine Fire engines arrive at the crash site. Hide Caption 39 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine A man stands next to wreckage. Hide Caption 40 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine Debris from the crashed jet lies in a field in Ukraine. Hide Caption 41 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine Family members of those aboard Flight 17 leave Schiphol Airport near Amsterdam, Netherlands. Hide Caption 42 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine A large piece of the plane lies on the ground. Hide Caption 43 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine Luggage from the flight sits in a field at the crash site. Hide Caption 44 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine A couple walks to the location at Schiphol Airport where more information would be given regarding the flight. Hide Caption 45 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine Flight arrivals are listed at the Kuala Lumpur International Airport in Sepang, Malaysia. Hide Caption 46 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine Debris from the Boeing 777, pictured on July 17, 2014. Hide Caption 47 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine A man inspects debris from the plane. Hide Caption 48 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine Wreckage from the plane is seen on July 17, 2014. Hide Caption 49 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine A man talks with security at Schiphol Airport on July 17, 2014. Hide Caption 50 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine Wreckage burns in Ukraine. Hide Caption 51 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine A man stands next to the wreckage of the airliner. Hide Caption 52 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine People inspect a piece of wreckage believed to be from Malaysia Airlines Flight 17. This image was posted to Twitter Hide Caption 53 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine People inspect a piece of wreckage believed to be from Malaysia Airlines Flight 17. This image was posted to Twitter. Hide Caption 54 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine A piece of wreckage believed to be from Malaysia Airlines Flight 17. This image was posted to Twitter Hide Caption 55 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine A piece of wreckage believed to be from MH17. This image was posted to Twitter Hide Caption 56 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine An airsickness bag believed to be from MH17. This image was posted to Twitter Hide Caption 57 of 58 Photos: Malaysia Airlines Flight 17 crashes in Ukraine A piece of wreckage believed to be from MH17. This image was posted to Twitter Hide Caption 58 of 58

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Bociurkiw said the OSCE had not confirmed whether the black boxes had been found.

"We will declare the black boxes found or located when we actually see them," he said.

The observers intended to ask whether they'd been found at the crash site on Sunday, he said, but "there was no one produced who could answer the question in a credible way."

Some Malaysian investigators flew to Kiev, the Ukrainian capital, on Saturday. But Malaysia's official news agency said they were still negotiating with rebels over access for their team.

Law enforcement officials from the Netherlands, the United States and Australia will help with the investigation led by the Ukrainian government.

Two FBI agents arrived in Kiev, a senior U.S. law enforcement official said. An investigator from the National Transportation Safety Board was also there.

But three days after the deadly crash, it was unclear when an international investigation at the scene would be able to start.

Families' agonizing wait

Journalist Noah Sneider, who's been covering fighting in Ukraine for months and was one of the first to arrive at the crash site on Thursday, said confusion at the scene is no surprise.

"All of this is happening in an active war zone. There's been a separatist uprising that began in April and has burned slowly up until this point. And security concerns are real, and the ability of any of the authorities on the ground here to effectively secure the area (is) minimal," he told CNN on Sunday. "The rebels are a patchwork group, and they seem to answer to different forces at different times."

For the families of the victims, the uncertainty only deepened their suffering.

Silene Fredriks said her son and his girlfriend had taken Flight MH17 for a planned vacation in Bali. At Amsterdam's Schiphol Airport on Sunday, she laid flowers and signed the condolence book.

She says she wants Russian President Vladimir Putin to ensure that the two young people's remains make it back to the Netherlands.

"I can do nothing but wait for their bodies," she said.

Pressure on Putin

Governments from around the world have expressed outrage at the disorderly situation at the crash site and called on Putin to use his influence on the rebels.

Cameron called Putin on Sunday to urge him to do what he can to ensure the victims "have proper funerals." His opinion piece urged Putin to find a way to make the crash site more accessible and calm the strife between Ukraine and the rebels.

"If President Putin does not change his approach to Ukraine, then Europe and the West must fundamentally change our approach to Russia," Cameron wrote.

Ten of the passengers on MH17, which was en route from Amsterdam to Kuala Lumpur, were British.

Australian Prime Minister Tony Abbott, whose country had 27 citizens on the plane, added to the pressure on Putin.

Describing the downing of the passenger jet as "a horrific crime," Abbott said he had summoned Russian Trade Minister Denis Manturov, who is visiting Australia, and "made crystal clear my concerns and dissatisfaction with the way this has been handled."

"Russian-controlled territory, Russian-backed rebels, quite likely a Russian-supplied weapon," Abbott said in a television interview Sunday. "Russia can't wash its hands of this."

Russia has denied any involvement, and Putin said Ukraine's military campaign against the rebels was to blame. He also has called for a "thorough and objective investigation" of the crash.

Finger-pointing

Since the crash, the Ukrainian government and the rebels have traded bitter accusations over who was responsible and what has been done since.

Ukrainian officials have said that a Russian-made Buk M1 missile system, brought into eastern Ukraine from Russia, had shot down the Malaysian airliner.

The Ukrainian government has accused the rebels of removing debris and 38 bodies from the scene as part of an attempt to cover up what happened.

Borodai has told reporters that the rebels lacked the firepower to hit an aircraft that high.

The United States has said evidence suggests a Russian-made surface-to-air missile fired from the rebel territory took down jet.

Kerry said a convoy of about 150 vehicles moved several weeks ago from Russia to eastern Ukraine. The military equipment included "multiple rocket launchers," he said.

"It's pretty clear that this is a system that was transferred from Russia in the hands of separatists," Kerry told CNN on Sunday.

A written statement from the U.S. Embassy in Kiev also included mention of Russia providing training to separatists at a facility in southwest Russia.

"This effort included training on air defense systems," the statement said.

U.S. officials believe the missile systems may have been moved back across the border into Russia.