(Reuters) - The Russian Defense Ministry said on Thursday that U.S. troops were training Ukrainian forces in the conflict zone in eastern Ukraine, but the Pentagon flatly denied it, accusing Moscow of a "ridiculous attempt" to obscure its own activity in the region.

Interfax quoted Russian Defense Ministry spokesman Major General Igor Konashenkov as saying U.S. troops were training Ukrainian forces not only in western Ukraine "as Ukrainian TV channels show, but directly in the combat zone in the area of Mariupol, Severodonetsk, Artyomovsk and Volnovakha."

The Russian Defense Ministry affirmed the report, but the Pentagon rejected it.

"This is a ridiculous attempt to shift the focus away from what is actually happening in eastern Ukraine," said Eileen Lainez, a Pentagon spokeswoman.

"Russia continues to supply lethal weapons, training and command and control support for armed separatists in eastern Ukraine, in blatant violation of Moscow's Minsk commitments and Ukraine's sovereignty," she added.

Lainez said the Pentagon had been clear about a program in which it was training Ukrainian guardsmen in the western part of the country.

The Pentagon announced on Monday that some 300 U.S. Army paratroopers from the 173rd Airborne Brigade based in Vicenza, Italy, had begun long-planned training for members of the Ukrainian national guard at the International Peacekeeping and Security Center at Yavoriv, near the Polish border.

The initial training involved 300 guardsmen and up to 900 were expected to be trained over six months, the Pentagon said. The focus was weapons handling, first aid, casualty evacuation and other small unit activity.

U.S. forces moved ahead with the training despite Russian warnings that it could be destabilizing. A European-brokered ceasefire is in force in eastern Ukraine but violations are reported daily.

Secretary of State John Kerry discussed the Ukraine situation with Russian Foreign Minister Sergei Lavrov in a phone call on Wednesday, urging Russia to press the separatists to abide by the ceasefire deal, a senior U.S. official said.

Kerry also insisted that Russia remove its forces from eastern Ukraine "where they continue to provide heavy weapons and training to separatists," the official added.

The official said the secretary made clear the U.S. training exercise was at the invitation of the Ukraine government and was "fully transparent, defensive."

Washington on Wednesday accused Russia of building up air defense systems inside eastern Ukraine and of involvement in training exercises of pro-Russian rebels in breach of the European-brokered truce.