The new US special representative for Ukraine says Washington is actively reviewing whether to send weapons to help those fighting against Russian-backed rebels.
Kurt Volker told the BBC that arming Ukrainian government forces could change Moscow’s approach.
He said he did not think the move would be provocative.
Russia warned that anything that heightened tension could jeopardise a solution to the conflict.
Mr Volker, a former US permanent representative to Nato, was given the role in Kiev earlier this month.
“Defensive weapons, ones that would allow Ukraine to defend itself, and to take out tanks for example, would actually help” stop Russia threatening Ukraine, he said in a BBC interview.
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“I’m not again predicting where we go on this. That’s a matter for further discussion and decision. But I think that argument that it would be provocative to Russia or emboldening of Ukraine is just getting it backwards,” he added.
He said success in establishing peace in eastern Ukraine would require what he called a new strategic dialogue with Russia. On a visit to the front line on Sunday Mr Volker had described the situation as a “hot war” that had to be addressed as quickly as possible.
Responding to Mr Volker’s latest remarks, Kremlin spokesman Dmitry Peskov told the BBC: “We have said more than once that any actions that provoke tension on the line of separation, that provoke a situation which is already complex, will only take us further away from the moment when this internal Ukrainian issue is resolved.”
The UN says more than 10,000 people have died since the eastern Ukraine conflict erupted in April 2014, soon after Russia annexed Ukraine’s Crimea peninsula. The fighting has displaced more than 1.6 million people.
A ceasefire was agreed in Minsk in February 2015, but its terms are far from being fulfilled. The leaders of France and Germany discussed the conflict over the phone with the presidents of Ukraine and Russia late on Monday.
There has been a sharp rise in violence in which eight Ukrainian soldiers were killed over 24 hours.
The US Department of State called it “the deadliest one-day period in 2017” in the eastern Ukraine conflict.