The black boxes for the downed Malaysia Airlines Flight MH17 have been found, a Ukraine rebel leader said Sunday.

Alexander Borodai said that the devices would be handed over to the International Civil Aviation Organization.

The announcement came as international investigators and Ukrainian officials said that pro-Russia separatists forced emergency services to surrender the bodies of 196 victims of the plane crash and loaded them onto refrigerated trains bound for a rebel-held city.

Borodai said the bodies would remain in refrigerated containers at a train station in the town of Torez until the arrival of an international aviation delegation.

The surprising, rapid-fire developments Sunday morning came after a wave of international outrage over how the bodies of plane crash victims were being handled and amid fears that the armed rebels who control the territory where the plane came down could be tampering with the evidence.

Ukraine and the separatists accuse each other of firing a surface-to-air missile Thursday at Malaysia Airlines Flight 17 as it flew from Amsterdam to Kuala Lumpur some 33,000 feet above the battlefields of eastern Ukraine. Both deny shooting down the plane. All those onboard the flight -- 283 passengers and 15 crew -- were killed.

Ukraine says Russia has been sending sophisticated arms to the rebels, a charge that Moscow denies.

The U.S. Embassy in Kiev issued a strong statement pointing to Russian complicity in arming the rebels, saying it has concluded "that Flight MH17 was likely downed by a SA-11 surface-to-air missile from separatist-controlled territory in eastern Ukraine." It said over the weekend of July 12-13, "Russia sent a convoy of military equipment with up to 150 vehicles, including tanks, armored personnel carriers, artillery and multiple rockets launchers" to the separatists. The statement also said Russia was training separatist fighters in southwest Russia, including on air defense systems.

The rebels have been strictly limiting the movements of international monitors and journalists at the crash site, which is near the Russian border, and Ukraine's Emergency Ministry said its workers were laboring under duress, overseen by the armed rebels.

Associated Press journalists saw reeking bodies baking in the summer heat Saturday, piled into body bags by the side of the road or still sprawled where they landed in the verdant farmland in eastern Ukraine after their plane was shot out of the sky.

By Sunday morning, AP journalists saw no bodies and no armed rebels at the crash site. Emergency workers were searching the sprawling fields only for body parts.

It was not immediately clear Sunday if the rebels and the Ukrainian government were working together or at odds with each other on recovering the bodies -- and from their comments, many of officials didn't appear to know either.

Separatists were not immediately available to comment Sunday. Despite the restrictions seen by journalists and observers at the crash site, Borodai insisted Saturday the rebels have not interfered with the work of observers.

Nataliya Khuruzhaya, a duty officer at the train station in Torez, 9 miles from the crash site, said she saw emergency workers loading plane victims' bodies Sunday morning into five sealed, refrigerated train cars.

She said the train was scheduled to head to the town of Ilovaysk, 22 miles further east toward the Russian border, but no instructions had been given about when it would leave or any possible destinations beyond Ilovaysk.

Russian news agencies said the bodies were heading to the rebel stronghold of Donetsk. Ukrainian officials say they expected to have the bodies eventually delivered to government-held city of Kharkiv, but it's unclear if the rebels will agree to do so.

Vasily Khoma, deputy of governor of the Kharkiv region where Ukraine has set up a crisis center to handle the disaster, said the Ukrainian state railway company had provided the refrigerated train cars. Kharkiv is 185 miles (300 kilometers) north of the crash site.

He said no information was available on when airplane parts would be brought to the city and that the priority now was on recovering bodies. He said a mobile lab to handle DNA analysis was being delivered from Dnipropetrovsk.

Residents in Kharkov have been inundating a special call center to offer their services as volunteers. Ten hotels in Kharkiv have said they will provide free rooms for relatives of the victims.

Earlier, Ukrainian Emergency Ministry spokeswoman Nataliya Bystro said workers at the crash site were forced to hand over the 196 bodies they had recovered to the armed rebels.

"Where they took the bodies -- we don't know," Bystro told the AP, adding she had no information about the other 102 victims' bodies.

However, Michael Bociurkiw, a spokesman for monitors from the Organization for Security and Cooperation in Europe, said some bodies have likely been incinerated without a trace.

"We're looking at the field where the engines have come down. This was the area which was exposed to the most intense heat. We do not see any bodies here. It appears that some have been vaporized," he told reporters in Kiev, speaking via phone from the crash site Sunday.

Alexander Pilyushny, an emergency worker combing the crash site for body parts Sunday morning, told the AP it took the rebels several hours Saturday to cart away the bodies. He said he and other workers had no choice but to hand over the bodies.

"They are armed and we are not," Pilyushny said.

In a blistering article for the Sunday Times, British Prime Minister David Cameron called the attack a "direct result of Russia destabilizing a sovereign state, violating its territorial integrity, backing thuggish militias and training and arming them."

"We must turn this moment of outrage into a moment of action," he wrote.

In a coded rebuke of German Chancellor Angela Merkel and other European leaders who have blocked efforts to impose tougher sanctions on Russian President Vladimir Putin for Russia's actions in Ukraine, Cameron said Europe must now "respond robustly."

"For too long, there has been a reluctance on the part of too many European countries to face up to the implications of what is happening in eastern Ukraine," Cameron wrote.

An Associated Press journalist saw a Buk missile launcher in rebel-held territory close to the crash site Thursday just hours before the plane was brought down.

Putin and Merkel agreed Saturday in a phone call that an independent commission led by the International Civil Aviation Organization should be granted swift access to the crash site.

Dutch Foreign Minister Frans Timmermans, speaking in Kiev, demanded that the culprits be found.

"Once we have the proof, we will not stop until the people are brought to justice," he said.

The Associated Press contributed to this report.