Ukraine yesterday said one of its soldiers was killed in fighting with pro-Moscow separatists, as the US again warned Russia against any attacks on the country.

US President Joe Biden was due to speak to his Ukrainian counterpart Volodymyr Zelensky today, after warning Russian President Vladimir Putin for the second time of a tough response should he invade Ukraine.

"One serviceman of the Joint Forces was fatally wounded," the army said in a statement, adding that separatists had launched three attacks within 24 hours, using grenade launchers and small arms.

The army gave no further details of how the soldier was killed.

Tensions with Moscow have soared in recent months, with Russia massing troops near Ukraine's borders. The West has accused the Kremlin of planning an invasion.