The Pentagon has alleged that Russia continues to provide the separatists fighting in eastern Ukraine with heavy weapons and other military equipment, in addition to financing.
"We see no hint that Russian support for the separatists has ceased. In fact, we believe that Russia continues to provide them with heavy weapons and other military equipment, financing as well. And they continue to allow these Russian fighters to enter Ukraine freely," Pentagon Spokesman Rear Admiral John Kirby told reporters.
"We have acknowledged that some tanks, some personnel vehicles have made their way across the border. It has been a steady, concerted campaign by Russia's military to continue to support and resource, advise these separatists," he said.
His remarks came after United States President Barack Obama pointed figure towards Russia-backed Ukrainian separatist for shooting down a Malaysia Airlines jet by a surface-to-air missile that killed all 298 people on board along the Ukraine-Russia border.
"We see strong evidence that Malaysia Airlines Flight MH17 was hit by a surface-to-air missile at an altitude of about 33,000 feet and that the missile was launched from a location near the border that is controlled by Russian separatists," Kirby said.
"This incident obviously occurred in the context of a conflict fuelled by Russian support for Ukrainian -- for these Russian separatists and that support has included arms, materiel and training," he alleged.
"As we investigate who did this and why, this terrible tragedy underscores the need for Russia to take immediate and concrete steps to deescalate the crisis in Ukraine and support the Ukrainian government's plan for a ceasefire and peace settlement," he said.
Kirby said, the missile itself, the SA-11, which is the one Pentagon believes was used to down Flight MH17, is a sophisticated piece of technology.
"It strains credulity to think that it could be used by separatists without at least some measure of Russian support and technical assistance," he stressed.
But he refrained from giving any evidence of this, when asked by reporters.
"There have been incursions across the border by Russian aircraft. We don't have any reason to suspect that they have not provided some measure of support on the other side of that order. These paramilitary forces that we do not talk about as much anymore certainly didn't act or behave or organise or resource like some ragtag militia," he said.
"So nobody is suggesting that Russian military advice and assistance hasn't somehow crossed that border. It's just unclear exactly how much and when and who. Again, that's what the investigators are going to look at and we've got to let them do that," Kirby said.
The United States, he said, is closely monitoring the situation along the Russia-Ukraine border in view of the shooting down of the Malaysian Airlines Flight 17.
Image: Members of the Australian Ukrainian community hold placards as they hold an anti-Russia rally in Sydney on Saturday.
Photograph: David Gray/Reuters