Russia said Monday it had handed over three navy ships it seized a year ago from Ukraine, in the latest move to ease tensions between the two countries ahead of a crucial summit.

Ukrainian President Volodymyr Zelensky denied Thursday that Donald Trump tried to blackmail him by withholding military aid to Kiev in a phone call between the two leaders. 

All 24 Ukrainians captured by Russia last year are expected to be part of an imminent prisoner swap between Kiev and Moscow, the head of their defence team told AFP on Saturday.

Ukrainian President Volodymyr Zelensky on Wednesday said he had asked his Russian counterpart Vladimir Putin to put pressure on separatist fighters in the east, after four Ukrainian soldiers were killed in a grenade attack.

Two Ukrainian soldiers and one civilian were killed in incidents involving Kremlin-backed separatists, Kiev said Saturday, a day before the country votes in a parliamentary election.

Three months after winning a landslide victory in Ukraine's presidential election, former comedian Volodymyr Zelensky is hoping to consolidate his success in parliamentary polls on Sunday. 

An army helicopter has crashed in western Ukraine killing four servicemen, the military said on Thursday.

Volodymyr Zelensky, a 41-year-old comedian who took office as Ukraine's president on Monday, announced the dissolution of parliament in his inaugural speech in order to hold early elections.

Three people have died and 14 are missing following a coal mine blast in a separatist eastern region of Ukraine, news agencies reported Friday. 

President Vladimir Putin said Thursday that Russia was ready to restore full relations with Kiev, after a political novice won the Ukraine presidential election.