KOSOVSKA MITROVICA, Kosovo - Serb demonstrators attacked international peacekeepers with rocks, grenades and Molotov cocktails Monday, setting off the worst violence in Kosovo since it declared independence from Serbia last month.

The Serbs traded gunfire with UN and NATO forces in hours of clashes that wounded at least 63 UN and NATO forces and 70 protesters outside a UN courthouse.

The clashes began when the UN stormed the courthouse in the divided northern town of Kosovska Mitrovica just before dawn to pull out protesters who had occupied it for three days to protest Kosovo's independence.

Hundreds of Serbs swarmed the area, blocking three red-and-white UN police vans as they moved through the angry crowd and ordering the officers to open the doors.

About half of the 53 arrested Serbs went free. The rest were taken out in armored vehicles and were released by the UN after questioning.

Danish military police said they came under fire from protesters and shot back as they evacuated wounded officers. Machine-gun bursts could be heard until midday, although it was not clear who was firing. At least one UN vehicle and one NATO truck were set ablaze.

The UN said later it was pulling out of the Serb-dominated northern half of the town because of the shooting.

NATO helicopters hovered above the city and NATO troops remained, but the UN withdrawal could fuel a widespread Kosovo Serb desire to split from largely ethnic Albanian Kosovo and rejoin Serbia.

Predominantly ethnic Albanian Kosovo has been under UN control since 1999, when NATO launched an air war to stop Slobodan Milosevic's crackdown on ethnic Albanian separatists.

Serbia, which considers the territory its historic and religious heartland, says Kosovo's declaration of independence was illegal under international law.

The Serb minority dominates about 15 percent of the territory in northern Kosovo, including about a third of Kosovska Mitrovica, Kosovo's second-largest city.

"We will protect you just like we protect the Serbs in Serbia," Slobodan Samardzic, Serbia's government minister for Kosovo, told the protesters.

He urged them to continue protesting with the goal of keeping Kosovo in Serbia. Monday's clashes came exactly one month after that Western-backed declaration.

"We will reach the goal only if we are patient, smart and organized and if we believe in what we want to accomplish," Samardzic said in the clearest indication yet that Serbia's government is orchestrating the protests.

Contributors to the NATO force said 27 Polish officers, 15 Ukrainians and about 20 French soldiers were wounded, with eight French troops taken to hospital. One of the French soldiers suffered head wounds from the explosion of a Molotov cocktail, though none had serious injuries. Authorities did not say how the other peacekeepers were wounded.

Hospital officials said most of the civilians suffered injuries from stun grenades, tear gas and explosive devices. One struck in the eye by a bullet was in critical condition.

UN Secretary-General Ban Ki-moon condemned the violence and pledged that the UN will continue "to take measures required to implement its mandate," to administer Kosovo, spokeswoman Michele Montas said.

The European Union and many of its members expressed concern and called for restraint. Germany urged international forces to get the situation under control, and said it would "not consider the division of Kosovo as an option."

Russia's UN Ambassador Vitaly Churkin, whose country has close ties to Serbia, expressed "serious misgivings" about the decision by UN police and NATO troops to storm the courthouse in the wee hours of the morning.

"Even if the takeover by the Serbs of the courthouse was unfortunate ... to us there are some very serious questions involved about the wisdom of such actions and lack of restraint," Churkin said.

Serbian President Boris Tadic accused international forces in Kosovo of "using excessive force," and warned of "escalation of clashes in the entire territory."

Serbia's Prime Minister Vojislav Kostunica said it was planning a joint response with Russia, Serbia's most powerful backer. Kostunica urged the UN Security Council to take "necessary steps" to restore security.

NATO's top commander said the alliance was not planning to send reinforcements to Kosovo.

"We are adequate for the task," Gen. John Craddock said in Afghanistan after speaking with NATO commanders in Kosovo.

In the Serbian capital, Belgrade, police deployed in front of government buildings and Western embassies, apparently fearing that rioting could erupt as it did in the days after Kosovo's declaration of independence on Feb. 17. Several thousand nationalists rallied downtown carrying Serbian flags and chanting "Kosovo is Serbia!"

Kosovo's Prime Minister Hashim Thaci said he regretted that Kosovo's minority Serbs were allowing themselves "to be manipulated by Belgrade" into engaging in violence.

"There will be no compromise with hooligans," Thaci said.