Russia's Foreign Minister Sergei Lavrov has called for "urgent measures for preventing an impending humanitarian catastrophe" in Ukraine during a telephone call with US counterpart John Kerry, his department says.
A statement from the Russian Foreign Ministry said Kerry "confirmed such work is being carried out with the Kiev authorities".
The statement follows reports that Ukrainian forces had surrounded the rebel-held city of Donetsk in the east of the country.
More top news
Rain across central Britain with longer, intense downpours with thunder in places this evening. A lucky few will stay sunny and dry.
Planning on going to the London Marathon tomorrow? Read our handy guide first!
Labour plans to cap above-inflation rent rises over a three-year period, if they win the General Election.