Russian President Vladimir Putin has urged Kyiv to allow Ukrainian soldiers who are encircled in an eastern Ukrainian town to lay down their weapons as Washington warned Moscow that "the costs to Russia will rise" if it kept supporting the rebels.
Fierce fighting for the strategic town of Debaltseve has continued despite a cease-fire agreement brokered by Germany and France last week.
A Ukrainian defense spokesman, Anatoliy Stelmakh, said "several (army) units were surrounded" in Debaltseve, as fighting for the strategic railway hub continued. Rebels have said Ukrainian forces must lay down their weapons in order to be allowed safe passage.
Putin, speaking on a visit to Hungary on February 17, said the conflict could not be solved by "military means."
Separatists said on February 17 that they seized most of Debaltseve and had surrounded the remaining government troops there. The rebels claim the truce does not apply to the battle front at Debaltseve.
The White House said U.S. Vice President Joe Biden, after talking on the phone with Ukrainian President Petro Proshenko, "strongly condemned the violation of the ceasefire by separatist forces acting in concert with Russian forces, in and around the town of Debaltseve," and warned of increased "costs" to Russia.