WASHINGTON, April 17 - The United States said on Thursday it would send Ukraine's armed forces medical supplies, sleeping mats and other non-lethal aid, seeking to signal support for Kiev while stopping far short of adding any U.S. weaponry to a deepening standoff with Russia, Reuters reported.

Defense Secretary Chuck Hagel made the announcement at the Pentagon as Kiev grapples with a pro-Russia uprising that has seen fighters seize whole swathes of Ukraine while Moscow masses tens of thousands of troops on the frontier.

Hagel voiced deep concern over "Russia's ongoing destabilizing activities in eastern Ukraine."

"De-escalation has been our focus and Russia must take steps to make that happen," he said.