Obama says burden on Russia to stop separatists from tampering with evidence in Ukraine plane crash

President Obama on Monday said “the burden now is on Russia” to stop separatists from tampering with evidence and allow international investigators access to the crash site of the downed Malaysia Airlines plane in Ukraine.

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“[Russian President Vladimir] Putin has direct responsibility to compel them to cooperate with the investigation,” Obama said during a brief statement from the White House.

Obama said international investigators have been denied access to the site “which begs the question, 'what exactly are they trying to hide?' ”

He added that pro-Russian separatists have been removing bodies from the site and called on Russia to step in.

“We have to make sure that the truth is out and that accountability exists in Ukraine,” he said.

His comments come as the United States tries to turn up the heat on Russia in the wake of Thursday’s downing of Malaysia Airlines Flight 17 that killed all 298 people on board, including one U.S.-Dutch citizen.

The White House has been calling for an international investigation into the incident and a cease-fire around the crash site, which has been littered with dead bodies, pieces of the plane, luggage and other personal effects of the passengers, including wallets, passports and clothing.

Pressure has been growing on Putin to rein in the insurgents in Ukraine and allow a full-scale investigation to take place. Russia has repeatedly denied backing the separatists.

The United Nations Security Council is slated to vote Monday afternoon on the draft resolution demanding international access to the site and a cease-fire around the area. The U.S. is pushing for a new round of aggressive sanctions against Russia.

But despite the powerful new impetus to act, there were questions over whether European leaders would at last agree on more-aggressive action and whether the U.S. and Europe would take the most economically punishing steps against Moscow. The sanctions imposed so far have been narrowly targeted and haven't applied to broad swaths of the Russian economy.

European Union diplomats said the 28-nation body could start freezing assets of companies and business people close to Putin as soon as Tuesday.

On Sunday, the United States presented what it called “powerful” evidence that pro-Russian rebels shot down the Boeing 777 with a surface-to-air missile.

“A buildup of extraordinary circumstantial evidence … it’s powerful here,” U.S. Secretary of State John Kerry said, pushing the narrative that Russia was involved.

“Russia is supporting these separatists,” he said. “Russia is arming these separatists. Russia is training these separatists.”

Among the evidence was a video of a rocket launcher, one surface-to-air missile missing, leaving the likely launch site, imagery showing the firing, phone calls claiming credit for the strike as well as phone recordings said to reveal an attempt at a cover-up at the crash site.

For his part, Putin lashed out against accusations his country was involved in the crash, accusing others of exploiting the downing of the plane for “mercenary objectives.”

Russian officials offered counter-evidence Monday against the U.S. allegations they are connected to the crash. The Russian Defense Ministry showed photos they claim prove Ukrainian surface-to-air systems were operated multiple times in the area in the days leading up to the Malaysian plane crash.

The Associated Press contributed to this report.