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.

A comedian with no political experience won a landslide victory in Ukraine's presidential election, drawing congratulations from global leaders while dealing a stunning rebuke to his country's political establishment. 

Ukrainians go to polls Sunday, with Volodymyr Zelensky, a 41-year-old comedian turned politician, set to win the leadership of a conflict-riven country seen as a buffer between Russia and the European Union.

Comedian Volodymyr Zelensky is favorite to become Ukraine's president after results Monday showed him dominating a first-round vote despite many initially dismissing his candidacy as a joke.