REPUBLIKA.CO.ID, KIEV -- Ukrainian forces released a separatist leader on Saturday after armed rebels attacked an eastern border post where he was being held, triggering a firefight, sources on both sides said.

Valery Bolotov, self-styled governor of the "Lugansk People's Republic" who is the subject of a Ukrainian arrest warrant, had been detained as he was trying to cross back into Ukraine from Russia, the border guard service said in a statement.

Scores of armed men surrounded the control post to demand the release of Bolotov, who rebels said had survived an "assassination attempt" earlier this week.

Bolotov had declared himself the governor of the eastern industrial region of Lugansk after separatists claimed victory in a hotly disputed May 11 referendum on independence from Kiev's rule.

After an hour of negotiations over Bolotov's fate, the rebels launched an assault, "shooting and hurling hand grenades", the border guards said.

Vasily Nikitin, spokesman of the self-proclaimed Lugansk People's Republic, confirmed that Bolotov had been released.

"They (the border guards) wanted to detain him at the border but our army was sent to free him," he told AFP. "He is free and with us."

Volodymyr Gromov, described as an official with the "southeastern army", said at a press conference that Bolotov had been released after a 15-minute gun battle, with 150 rebels facing off against about 80 border guards, according to the Interfax Ukraine news agency.

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