“Based on Russia's effort to escalate the situation militarily, we have seen the continued movement of equipment and material across the border from Russia into Ukraine,” the White House Press Secretary Josh Earnest told reporters at his daily news conference.

“We've even seen pretty definitive reports that Russian troops are now firing on Ukrainian military positions. The international community is completely unwilling to tolerate Russian interference in Ukraine,” Earnest added

The White House official warned of “additional economic costs that can be imposed by the United States on Russia”.

Earnest also commented on the findings by NATO that claimed that Russia had sent at least 1,000 troops to fight with pro-Moscow rebels in Ukraine, along with air defence systems, artillery, tanks and armored vehicles; and had massed 20,000 troops near the border.

“The evidence that has been presented by NATO is compelling. It does indicate that Russia is continuing to do the kind of things for using their military might to further destabilize the situation in Ukraine,” he said.

The official urged “Russia to use their influence in Ukraine to try to deescalate the situation.”

Earnest also lashed out at Russia for denying its role in the escalating tension in Ukraine.

“As the Russian military has allowed weapons and material to be transferred across the border, fired on Ukrainian military positions and put boots on the ground in Ukraine; we have regularly marshaled evidence to indicate what exactly is happening, despite the protestations of the Russian government.”

“The denial by the Russian government is without any credibility, and we've been pretty candid about that,” Earnest said.

Talking about the visit of US President Barack Obama to Europe next week for NATO meeting, the official said “The situation in Russia would be on top of the agenda of the US President when he travels to Europe next week,” he said.

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