The United States has expressed concern over the concentration of Russia troops along the Ukrainian border and warned that any movement of Russian troops into Ukraine would be "a grave mistake," State Department's spokesperson Jen Psaki said.

"Any movement into Ukraine would be a grave mistake," Psaki said at a daily briefing in Washington on Thursday.

She said that since the signing of the Geneva agreements on April 17, U.S. State Secretary John Kerry has spoken with Russian Foreign Minister Lavrov six times about the de-escalation of the Ukrainian crisis. However, Lavrov "has never once taken responsibility for the implementation of Russia's Geneva commitments. Indeed, he's gone so far as to say the Geneva agreement demands no action from Russia, and that instead this is an internal Ukrainian issue."

Psaki said that the United States doesn't put all the responsibility for the settlement of the situation in Ukraine on Russia.

"I don't think it's putting all responsibility on Russia at all… There were steps agreed to by both the Ukrainians, which they have abided by, and steps agreed to by the Russians, which they have not. It's as simple as that," she said.

Commenting on anti-terrorist operations in eastern she said that Ukraine's government is the legitimate government of the whole of Ukraine.

"They have the right to maintain calm, maintain stability, maintain order in their country," she said.