Update 11:35 AM EDT: President Obama spoke harshly of Russia and President Vladimir Putin's role in the MH17 crisis, directly accusing him of supplying them with arms, training and personnel.
"Russia has urged them on, has trained them, has armed them with military equipment and weapons, including anti-aircraft weapons," Obama said.
Obama said definitively that separatists were "removing evidence from the crash site, which begs the question, what are they trying to hide?"
The president warned that if Russia continued its support of separatists, the international community would continue with sanctions and Russia "will only further isolate itself."
He said he still believes there is a diplomatic solution to the crisis.
President Barack Obama spoke about Ukraine on Monday, four days after Malaysia Airlines Flight MH17 was shot down over contested territory in the country last Thursday.
Ukrainian officials have placed the blame on Russia for the downing of the aircraft, which was hit by a missile from a Russian-made Buk missile system. Russia was quick to rebuke those claims and instead alleges the plane was brought down by the Ukrainian military. All 297 passengers aboard MH17 were killed in the downing.
Obama has insisted that pro-Russian rebels, who currently control the crash site, not interfere with an international investigatory team.