(Adds at least two killed, quotes, changes dateline)
* Clash takes place two days before election
* Separatists have vowed to disrupt poll in the east
By Sabina Zawadzki and Gabriela Baczynska
KARLOVKA, Ukraine, May 23 (Reuters) - Armed pro-Russian separatists clashed with Ukrainian self-defence fighters near the eastern city of Donetsk on Friday, two days before the presidential election, and at least two people were killed, a Reuters witness and militia sources said.
A leader of a Ukrainian militia group said his men had been on a reconnaissance mission near the rural settlement of Karlovka, about 15 km (10 miles) west of Donetsk, when it ran into a checkpoint manned by heavily-armed separatists.
The clash, after the deaths of at least 13 Ukrainian servicemen on Thursday in another firefight in the locality of Volnovakha, suggested there would be no let-up in violence in the east during Sunday's election.
Kiev's pro-Western government hopes the election will stabilise Ukraine after mass street protests toppled Moscow-backed president Viktor Yanukovich in February, but the separatists have vowed to prevent the vote going ahead in eastern towns where they have seized control.
In a firefight that lasted more than three hours, according to locals, separatists on Friday used automatic weapons, snipers and grenade-launchers, according to Semen Semenchenko, commander of the so-called Donbass region battalion, a pro-Ukrainian militia force.
"We have so far confirmed one dead from our soldiers. We hope the others have been captured but if they are not we will have up to five dead. We have more than five injured, they are being taken away to Kiev now," Semenchenko told Reuters.
In Karlovka itself a Reuters correspondent saw two dead men both dressed in black battle fatigues. One lay on his back by the roadside while another lay some distance away near a burned-out warehouse. He had a gunshot wound in his head.
Another fighter, dressed also in battle fatigues, was clenching his fists in pain as he was being tended to by paramedics for leg wounds.
Russia annexed Ukraine's Crimea region after Yanukovich was overthrown and refuses to recognise the legitimacy of the new leadership. But it denies Kiev's charges that it has fomented the separatist rebellions in the Russian-speaking east.
"A small unit was on the road doing reconnaissance and it ran into a roadblock where there were many more separatists than us. They opened sniper fire, they had armoured personnel carriers and machineguns," Semenchenko said.
He alleged that the separatists included at least 15 Chechen fighters from Russia's former rebel region of Chechnya. "We will now eliminate their roadblock with aerial forces," he said.
There was no immediate account from the separatists of the incident and it was not clear who opened fire first.
Locals who had largely stayed indoors as soon as the shooting began in the early morning were unclear about who had attacked whom and had a mixed view of who was to blame.
A 52-year-old woman who gave only her first name of Valentina laid the blame at the door of Kiev which is using the Ukrainian army in an "anti-terrorist operation" to end an insurgency in which armed separatists have taken control of strategic buildings in several towns including the industrial hub of Donetsk where they have proclaimed a "people's republic".
"Why do they (the Kiev authorities) do this? Why is Europe silent? Everybody was living normally but now everyone is interfering".
Asked if she would vote on Sunday, Valentina said: "Who should I vote for - for people who are killing us and shooting at us? The answer is No!".
Alexei, in nearby Krasnomaisk, voiced an opposite view as he brought petrol to pro-Ukrainian self-defence fighters.
"All this is because these idiot separatists want to undermine the elections. But we will vote anyway. Out of 25 kids in my son's school, only seven are for Ukraine, the others call my son 'Banderovets'," he said, referring to a pejorative label for ultra-nationalist.
In Kiev, authorities who are hoping for a big turnout despite the loss of Crimea and separatist opposition said they would press on with election preparations.
"We understand that Kiev, western and central Ukraine do not represent the whole country. Armed groups which are operating in the east are trying all they can to stop the electoral process. They are seizing buildings, wrecking (electoral) technology and abducting people in efforts to intimidate people," deputy prosecutor general Mykola Holomsha told journalists.
State Security chief Valentyn Nalivaychenko said separatist plans to disrupt the count by using a computer virus had been stopped. "We destroyed a computer programme yesterday that was to have wrecked the results of the election," he said.
(Writing By Richard Balmforth; Editing by Janet Lawrence)
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