US Secretary of State John Kerry warned Russia that it must not intervene in Ukraine under the "pretext of peacekeeping", his department said.
The statement follows Russia's version of the call, in which its Foreign Minister Sergei Lavrov was said to have called for urgent measures to avert a "humanitarian catastrophe" in the east of the country.
More top news
The Duke of Cambridge became a fearsome samurai warlord - at least temporarily - when he visited the set of a long-running Japanese drama.
A grandmother says she was outraged after her grandson was segregated from his classmates by a cardboard screen - for being one minute late.
Leaked documents have revealed the first known picture of Mohammed Emwazi - named as IS militant Jihadi John - as a student in London.