A voter casts a ballot during a referendum in the eastern Ukrainian city of Slaviansk May 11, 2014
Voting began on Sunday in referendums called by pro-Russian rebels in eastern Ukraine to split from the rest of the former Soviet republic, polls the US slammed as "illegal" amid fears they could spark civil war.
They come as fighting continued in eastern Ukraine, with several explosions heard overnight in the flashpoint town of Slavyansk as the Kiev authorities try to flush the rebels from towns they control.
The vote, carried out as two "referendums" in provinces where the insurgents hold more than a dozen towns, marks a serious deepening of the political crisis in Ukraine, which has pushed East-West relations to lows not seen since the end of the Cold War.
Although a "yes" vote would likely be recognised only by Russia, it would greatly undermine a presidential election Ukraine is to hold in two weeks, which the United States and the European Union see as crucial to restoring stability.
Ukrainian troops have been battling the well-armed separatists, who have barricaded themselves in towns and cities in the two provinces where the votes are taking place: Donetsk and Lugansk.
In Mariupol, scene of recent fierce fighting between Ukrainian troops and pro-Russian militants, queues of hundreds of people snaked towards the polling stations, an AFP reporter on the scene said.
"I want to be independent from everyone," said ex-factory worker Nikolai Cherepin. "Yugoslavia broke up and they live well now".
Tatiana, a 35-year-old florist voting in the regional hub of Donetsk, told AFP: "We have come to fight for our rights and become independent and we are happy that we've been given the right to voice our opinion."
"If we're independent, it will be hard at the beginning but it will be better than being with the fascists," she added, using a term frequently used by separatists to describe the Western-backed government in Kiev.
- US slams 'illegal' vote -Ahead of the referendums, US State Department spokeswoman Jen Psaki said they were "illegal under Ukrainian law and are an attempt to create further division and disorder".
The votes "violate international law and the territorial integrity of Ukraine," she stressed, adding that the United States would not recognise the result.
On Saturday, France and Germany jointly threatened "consequences" on Russia if the presidential election is scuppered - echoing US President Barack Obama's warning of automatic sanctions that would slice into whole sectors of Russia's weakening economy.
Interim Ukrainian president Oleksandr Turchynov warned that voting for independence would be a "step into the abyss" for these regions and lead to the "total destruction" of the economy there.
- '100 percent turnout' -Despite rebel claims that the polling will reach 90 percent of the seven million people living in these two provinces, the areas they hold account for less than half that population.
They decided to go ahead with the vote despite a public request made Wednesday by Russian President Vladimir Putin to postpone it.
Polling stations opened in schools in rebel-held territory at 8:00 am (0500 GMT) and were to close 12 hours later, according to insurgent chiefs in the city of Donetsk.
The self-proclaimed mayor of Slavyansk, Vyacheslav Ponomaryov, said he expected 100 percent turnout for Sunday's vote.
After the results come in, "the Republic of Donetsk will begin to function" and cultivate "friendly relations" with Russia, he added.
But another rebel leader, Roman Lyagin, said: "If the answer is yes, it does not necessarily mean that we will be joining Russia".
A poll released Thursday by the Pew Research Centre in the United States suggested 70 percent of Ukrainians in the east want to stay in a united country, while only 18 percent back secession.
Kiev has already dismissed the vote as "illegitimate" and against the Ukrainian constitution.
However, like in Crimea -- which Russia annexed in March after a similar referendum -- it has been powerless to stop it.
- West threatens 'consequences' -The Ukrainian government and its Western backers accuse Putin of deploying Russian special forces in east Ukraine, as in Crimea, to see the vote through and to sabotage the May 25 presidential election.
Putin belatedly admitted sending military forces to Crimea but continues to deny militarily meddling in east Ukraine.
In their joint statement Saturday, French President Francois Hollande and German Chancellor Angela Merkel urged Ukraine's security forces to stop their offensive on rebel-held positions in order to give dialogue a chance.
That echoed a call by Putin, who set that as his condition for backing the presidential election.
But, the leaders of France and Germany warned, if the subsequent presidential election was stymied, "appropriate consequences should be drawn," indicating tougher sanctions in line with those brandished by the United States. The vote added fuel to a crisis that has turned increasingly deadly in the past two weeks.
On Friday, several people were killed in what Interior Minister Arsen Avakov said was a "full-scale military clash" in the southeastern port city of Mariupol, as Ukraine and Russia commemorated the Soviet victory over German forces in World War II.
Mariupol on Sunday observed a day of mourning, and an AFP reporter said passions remained high.
It appeared to be the bloodiest day in the conflict since May 2, when clashes that resulted in a horrific inferno in the southern port city of Odessa claimed another 42 lives, most of them pro-Russian activists.
Ukrainian authorities initially put the number of dead at more than 20 but some observers on the ground, such as Human Rights Watch, have said there is no proof that more than 10 people were killed.