The behavior of Russian-backed separatists controlling the Malaysia Airlines Flight 17 crash site in Ukraine "begs the question, what exactly are they trying to hide?" Obama said today.
The president said that the separatists and their "Russian sponsors" must allow investigators "immediate, full, and unimpeded access" to the wreckage of the downed plane.
"We have to make sure that the truth is out and that accountability exists," he added. "Our immediate focus is on recovering those who were lost, investigating exactly what happened, and putting forward the facts."
Separatists Have 'Full Control' Over MH 17 Crash Site, Says Malaysian Minister
'Enormous Array of Facts' That Russia Supported Rebels Accused of Shooting Down Plane, Says John Kerry
Australian Newlyweds Escape MH17 Tragedy
Investigative teams are standing by, ready to scour the crash site, Obama said, but pro-Russian separatists are preventing the investigators from entering the crash zone, allegedly tampering with evidence and even removing bodies without proper care.
Separatists' refusal to allow workers to recover the victims' remains "is an insult to those who've lost loved ones ... the kind of behavior that has no place in the community of nations," Obama said.
Obama, who last week pledged the support of the NTSB and FBI, called on Russia to urge separatists to back off.
"Russia has extraordinary influence over these separatists. No one denies that," said Obama. "Russia has urged them on. Russia has trained them. We know that Russia has armed them with military equipment and weapons, including anti-aircraft weapons ...Given its direct influence over the separatists, Russia, and President Putin in particular, has direct responsibility to compel them to cooperate with the investigation."
"If Russia continues to violate Ukraine's sovereignty and to back these separatists ... then Russia will only further isolate itself from the international community and the costs for Russia's behavior will only continue to increase," he said. "Now is the time for President Putin and Russia to pivot away from the strategy that they've been taking and get serious about trying to resolve hostilities within Ukraine."
U.S. intelligence suggests Russia may have armed and trained the separatists accused of shooting down the jet, officials say.
"There are an enormous array of facts that point at Russia's support for and involvement in this effort," Secretary of State John Kerry told ABC News' George Stephonopolous on "This Week" Sunday.
Given the separatists' irreverent treatment of the crash site, Russia must "step up and be part of the solution, not part of the problem," Kerry said.
"President Putin should publicly call on the separatists. He should engage in a public support for the cease-fire," he added.
Senate Intelligence Committee Chairwoman Dianne Feinstein, D-Calif., was less circumspect, calling on Russian President Vladimir Putin to "man up" on CNN Sunday.
"I would say, Putin, you have to man up. You should talk to the world. You should say this was a mistake, if it was a mistake," she said.
Obama On Russian Separatists: 'What Exactly Are They Trying To Hide'