The US has described as "a good, tiny first step" Ukrainian President Petro Poroshenko's announcement that Russia has withdrawn the bulk of its forces from his country.
Washington was unable to verify what would be a potentially significant development in the crisis, State Department spokeswoman Marie Harf said, adding: "If it is correct - but it is far from enough - it would be a good tiny first step."
Poroshenko said Friday's ceasefire - the first backed by both Kiev and Moscow since the conflict erupted five months ago - had dramatically improved security in Ukraine's industrial rustbelt, where Kiev has been battling pro-Moscow rebels.
Giving a cautious welcome to the apparent Russian withdrawal, Harf added: "Of course, even if we eventually can verify his claims about the Russian troops pulling back, there would still be Russian troops that remain there.
"Obviously, any de-escalatory steps would be good ones, but there is much more work to be done here.".
Speaking separately, at the German Marshall Fund in Washington, Victoria Nuland, assistant secretary of state for European and Eurasian affairs, cautioned that "there is a long road to go".
"All foreign forces have to be withdrawn, all foreign material has to be withdrawn, the border has to be secured, there has to be the decentralisation and amnesty that have been promised," she said.
