Interim Interior Minister Arsen Avakov wrote Friday on Facebook that a secessionist attempt to seize police headquarters in Mariupol had turned into a pitched battle inside the building with the army, national guard and police battling separatists. The Ukrainian forces brought armored personnel carriers into the town and the building caught fire at one point. The rebels then fled.

"A terrorist group of about 60 men armed with automatic weapons attacked the police headquarters ..." Avakov wrote on his Facebook page. "About 20 terrorists were destroyed and four taken prisoner. To those who come with weapons and who shoot and who take hostages, torture them, rob people, hiding behind various slogans - to them there can be only one answer from the Ukrainian state - annihilation."

Friday's clashes come amid attempts to prevent a slide into a civil war. Mariupol, a city of about 500,000 people on the Azov Sea and an important industrial and shipping center, has become the focus of frequent skirmishes in recent days. With Friday's actions, security forces appear to have begun using everything at their disposal to claw back control from the separatists.

The separatist-led Donetsk regional administration has claimed the operation killed three people and left 25 wounded during the fighting. If the interim government can confirm the higher death toll announced by Avakov, it would prove among the heaviest inflicted on the secessionists during fighting. Avakov also wrote that one member of the security forces was killed and five more injured during the operation.

'Unauthorized local referenda'

On Friday, EU representatives said Sunday's votes, in which up to 3 million could vote on seceding from Ukraine, would further complicate the standoff. Separatist leaders had said on Thursday that they would go ahead with the referenda despite an appeal by Russian President Vladimir Putin to postpone them.

"Such unauthorized local referenda have no democratic legitimacy and can only lead to further escalation," EU spokeswoman Maja Kocijancic said on Friday.

Chancellor Angela Merkel planned to discuss the standoff in Ukraine with French President Francois Hollande during his weekend visit to Germany, which began Friday afternoon.

The tensions coincide with the May 9 celebrations of the Soviet Union's 1945 defeat of Nazi Germany to end World War II. Russian President Vladimir Putin made a surprise appearance in Crimea, which his country had quickly annexed after it voted to secede from Ukraine in March.

Fears arose on Friday that celebrations within Ukraine's current borders could degenerate into nationalist violence. Interim president Arseniy Yatsenyuk said festivities would take place "under war conditions."

mkg/msh (Reuters, AFP, dpa, AP)