Updated at 4:25 p.m. ET.

In the most emphatic U.S. statement to date on culpability for the downing of a Malaysian airliner over Eastern Ukraine that killed 298 people, Secretary of State John Kerry says evidence overwhelmingly points to Russian-backed separatists.

In an interview with CNN, he says that U.S. intelligence, as well as social media put out by the rebels, "obviously points a very clear finger at the separatists."

Kerry said the rebels had used social media to brag about shooting down the plane Thursday until they realized it was a commercial jetliner.

He also noted a steady flow of Russian arms over the border to supply the rebels in the past month and said the separatists had shot down a dozen aircraft over that time period.

"It's pretty clear that this is a system that was transferred from Russia," Kerry tells CNN.

A rescue worker walks across a field carrying what appears to be a flight data recorder at the crash site of Malaysia Airlines Flight MH17 in Hrabove in this still image taken from a video. (REUTERS TV/Reuters/Landov)

"We know with confidence — with confidence — that the Ukrainians did not have such a [surface-to-air missile] system in the area at the time this occurred," he said.

"Drunken separatists have been piling bodies into trucks and removing them from the site," Kerry said on NBC on Sunday. "What's happening is really grotesque and it is contrary to everything President Putin and Russia said they would do."

That outrage over the handling of remains and the inability of international teams to get unfettered access to the crash site of Malaysia Airlines MH17, is increasingly focusing on Moscow, with Britain's prime minster blasting the Kremlin in an editorial.

"[This] is a direct result of Russia destabilising a sovereign state, violating its territorial integrity, backing thuggish militias and training and arming them," he wrote in the Sunday Times, referring to Moscow's support of pro-Russian separatists in Ukraine.

The harsh words come amid reports that separatist rebels in the area where the plane was brought down Thursday had taken dozens of bodies from the crash site where 298 people were killed.

The BBC says, "International monitors were informed that 169 had been moved to the train in the nearby town of Torez."

USA Today says: "Reports Saturday of how the bodies were decaying in Ukraine fields drew strong outrage worldwide, especially from the Netherlands, home to over half the victims. 192 bodies have been recovered from the crash site so far."

Dutch Foreign Minister Frans Timmermans said the Netherlands was "angry, furious" over news that bodies were being moved at the crash site and not being treated properly, Reuters reports.

"We are already shocked by the news we got today of bodies being dragged around, of the site not being treated properly," he said.

Meanwhile, a separatist rebel leader says the flight data recorder from the Boeing 777 has been recovered and would be handed over to international aviation authorities.

"Some items, presumably the black boxes, were found, and they have been delivered to Donetsk and they are under our control," Aleksander Borodai, prime minister of the self-styled Donetsk People's Republic, told a news conference.

A conference attendee ties a ribbon in tribute to those who lost their lives on flight MH17 during the International AIDS Conference in Melbourne on Sunday. At least six delegates traveling to the conference were on board. (Graham Denholm/Getty Images)

"There are no specialists among us who could pinpoint the look of the black boxes, but we brought to Donetsk some technical items which could be the black boxes of the airliner," Borodai said, according to Reuters.

In other developments:

-- Borodai is telling the media that the rebels will guarantee the safety of crash site observers in exchange for a Kiev-backed truce, says The Guardian.

Ukraine President Petro Poroshenko told Reuters, "We will not tolerate interference with the work of the commission."

-- The U.N. Security Council is considering an Australian-drafted resolution condemning the "shooting down" of the airliner. The resolution would also demand armed groups allow access to the crash site and call on states in the region to cooperate with the international investigation.

The draft is being circulated to Security Council members and diplomats by Australia, which lost 28 citizens.

-- The International AIDS Conference begins in Melbourne, under the grim shadow of the crash and with some of its top thinkers missing. Six AIDS researchers and advocates were aboard the plane, bound for the conference.

"Those on MH17 all worked so hard in the science and community response to HIV — losing all six of them is a major loss," conference co-chairwoman and professor of infectious diseases Sharon Lewin told The Guardian.

Conferees will pay respects to the dead at the opening ceremony Sunday night with one minute of silence.

"Everyone is devastated, of course, and it's not just an accident — it's a direct killing, it's murder, which makes it even more gruesome," said the director of Dutch HIV support organization Ton Coenen.

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