U.S. Secretary of State John Kerry arrived in snowbound Kiev on Thursday amid calls for Washington to begin arming Ukraine to battle Russian-backed separatists advancing in the east.
NATO says Russia has sent weapons, funds and troops on the ground to assist the rebel advance, which scuppered a five-month-old ceasefire in eastern Ukraine where war has already killed more than 5,000 people.
Moscow denies involvement in fighting for territory the Kremlin now calls "New Russia".
Washington has given its clearest signal yet that it is considering providing weapons to Ukraine. President Barack Obama's pick for defense secretary, Ashton Carter, told a Senate committee he would "very much incline" toward supplying arms to Ukraine.
"The nature of those arms, I can't say right now," Carter said at his Senate confirmation hearing. "But I incline in the direction of providing them with arms, including, to get to what I'm sure your question is, lethal arms."
Asked about the risks of escalation, he said: "I think the economic and political pressure onRussia has to remain the main center of gravity of our effort in pushing back."
Kerry's visit is more about diplomatic support for now. U.S. officials said he would promise $16.4 million in humanitarian aid, barely a token gesture for a country that is in desperate need of billions in overseas financing to stave off the threat of bankruptcy, worsened by war.
Western advocates of arming Ukraine say it would help raise the costs for President Vladimir Putin of pursuing Russia's objectives. Opponents worry about escalating a conflict that would see NATO and Russia actively aiding opposing sides in battle for the first time since the Cold War.
Ukraine's President Petro Poroshenko called unambiguously for NATO arms in an interview with a German newspaper.
"The escalation of the conflict that's happening today, the increasing number of civilian casualties... should move the alliance to provide Ukraine with more support," Poroshenko told Die Welt. "(That) includes, among other things, delivering modern weapons for protection and for resisting the aggressor."
But some NATO members are opposed to sending weapons.
"This is not a solution that could involve the European Union or our country in the slightest," Italy's Foreign Minister Paolo Gentiloni said in a radio interview. The EU should maintain pressure through sanctions, not weapons, he said.
The rebels have been concentrating their advance on Debaltseve, a rail hub between their two main strongholds of Donetsk and Luhansk, where a government garrison has held out despite being nearly encircled.
On Wednesday, the rebels appeared to have captured Vuhlehirsk, a nearby small town where government troops had also been holding out. The army said it was still contesting the town, but Reuters journalists who reached it saw no sign of areas under army control.
Some of the residents who had not fled the shattered town came out of cellars where they had been holed up through days of fighting. Four dead Ukrainian soldiers lay in a garden.
"Someone should come to remove these corpses, it is inhumane to leave them here to rot," said Sergey Kopun, 50, a metal worker, who emerged from the cellar where he had sheltered with his wife and quadriplegic mother.
In Kiev, the military said on Thursday five more soldiers had been killed and 29 wounded in the past 24 hours. Troops had fended off two attempts to storm Debaltseve.
The war and years of endemic corruption have brought Ukraine to the verge of economic collapse and bankruptcy.
The central bank announced an sharp hike in interest rates on Thursday, boosting the key re-financing rate to 19.5 percent from 14 percent, to stave off the collapse of the hryvnia currency.
"There is still panic on the market, connected with ongoing fighting," Central Bank governor Valeria Gontareva told a news conference.
