US President Barack Obama has piled pressure on Russian President Vladimir Putin to force pro-Russian separatists on Monday, report Reuters.
The separatists are hampering the international investigation into the shoot down of a passenger jet last week, he claimed.
Obama denounced the Russian role in eastern Ukraine with tough connotation.
He asked Putin to cut ties with the separatists or risk greater international isolation.
"Now is the time for President Putin and Russia to pivot away from the strategy that they have been taking and get serious about trying to resolve hostilities within Ukraine," US president said in remarks on his speech.
Investigators are blocked from access to the crash site in eastern Ukraine and most of the bodies of the victims were removed by the separatists.
Obama said Russia should compel the separatists to let the investigation take place.
He questioned about the intention of the separatists adding, “What are they trying to hide?"
Obama did not specifically threaten new economic sanctions against Russia, but he hinted at costs to come should Moscow not change course.
"The costs for Russia's behaviour will only continue to increase," he said.
US officials are increasingly confident that the Malaysian Airlines plane was shot down by the separatists with a Russian-made surface-to-air missile.
Given Russia influence over the rebels, Obama said, "Russia, and President Putin in particular, has direct responsibility to compel them to cooperate with the investigation. That is the least that they can do."
"President Putin says that he supports a full and fair investigation, and I appreciate those words, but they have to be supported by actions," he added.