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. 

President Vladimir Putin on Wednesday signed a decree making it easier for people living in eastern Ukraine's separatist territories to obtain a Russian passport.

The decree, published on the Kremlin website, is aimed at residents of the unrecognised Donetsk and Lugansk republics that broke away from Kiev in 2014 and are governed by Moscow-backed rebels.

Ukraine leapt into the unknown Monday after comedian Volodymyr Zelensky was elected president on promises of change but with just a vague blueprint of what he might do as leader.

German Chancellor Angela Merkel on Monday congratulated comedian Volodymyr Zelensky on his landslide victory in Ukraine's presidential election, saying she hopes the vote will help stabilise the troubled country.

"I congratulate you on your election," Merkel said in a statement.