Pro-Russian separatists in eastern Ukraine began voting in controversial leadership elections on Sunday that Kiev and the West have refused to recognise and which threatened to deepen an international crisis over the conflict.

The elections in the self-declared Donetsk People's Republic and Lugansk People's Republic, which are based around the two main rebel-held cities, were designed to bring a degree of legitimacy to the makeshift military regimes that already control them.

However, heavy fighting flared across the conflict zone in south-eastern Ukraine ahead of the election, which Ukrainian President Petro Poroshenko has blasted as a violation of an already tattered truce deal signed on September 5.

Russia, which supports the rebels but denies fighting on their side, says it will recognise the results of the elections. The United States and European capitals, which have imposed heavy economic sanctions on Russia, back Kiev in condemning the polls as illegal.

Both self-declared republics were choosing new presidents and parliaments, but there was little question that the current unelected rebel chiefs -- Alexander Zakharchenko in Donetsk and Igor Plotnitsky in Lugansk -- would be confirmed in their posts.

No international election monitors were present for the vote, and no minimum turnout has been set by the organisers, reflecting the uncertainty over how many voters could turn out.

"These elections are important because they will give legitimacy to our power and give us more distance from Kiev," said Roman Lyagin, election commission chief of the Donetsk People's Republic.

Poroshenko called the polls "pseudo-elections that terrorists and bandits want to organise on occupied territory."

The war has killed more than 4,000 people, including more than 300 in the last two weeks, since erupting in April. A month earlier, Russian troops invaded Ukraine's southern province of Crimea, which was then annexed by Moscow.

Polls opened at 5:00 GMT and were to close at 17:00 GMT.