Washington, Nov 10 (IANS): The US is "very concerned" by intensified fighting and rebels' military build-up in eastern Ukraine, the White House said Sunday.

"Any attempt by separatist forces to seize additional territory in eastern Ukraine would be a blatant violation of the Minsk agreements," reported Xinhua citing a statement issued by Bernadette Meehan, spokesperson for White House's National Security Council.

The Ukrainian government and the rebels inked a ceasefire agreement Sep 5 in Minsk, capital of Belarus, at a meeting also attended by envoys from Russia and the Organization for Security and Cooperation in Europe (OSCE).

The separatists are moving large convoys of heavy weapons and tanks to the front lines of the conflict in eastern Ukraine, Meehan said, citing reports from (OSCE).

The US reiterates the call on Russia to honour all the commitments it made in Minsk, including ending its military supply to the separatists and the withdrawal of all of its troops and weapons from Ukraine, said Meehan.

The US continues to stress that adherence to the framework agreed upon in Minsk is the best chance of achieving a peaceful resolution to the conflict in eastern Ukraine, the spokesperson added.

Moscow has denied the Western allegation that it aided the rebels militarily in the conflict.