Angered by ethnic clashes in Kosovo that targeted their kin, Serb nationalists rampaged Thursday in Serbia, torching mosques and threatening Kosovo's ethnic Albanians with "slaughter and death."

The protests in Belgrade (search) and other Serbian towns were reminiscent of similar nationalist outbursts at the start of the Balkan wars in the early 1990s, when former President Slobodan Milosevic's propaganda deliberately incited hatred toward other ethnic groups then living in the former Yugoslavia.

Overnight in Belgrade, the capital of Serbia-Montenegro, demonstrators set a 17th century mosque — the city's sole place of worship for Muslims — on fire after clashing with police trying to guard the building.

The head of Serbia's Muslim community, Hamdija Jusufspahic (search), criticized the police for their "passive" protection of the mosque, which remained intact during the Serb-Muslim war in Bosnia but was gutted early Thursday with only its stone walls remaining.

"Sadly, there is no more place for worship for the Islamic community in Belgrade, and that is a shame for those who could have prevented it," Jusufspahic said.

Demonstrators demanded that the government act to protect their Orthodox Christian (search) kin in Kosovo from attacks by the province's predominantly Muslim ethnic Albanians.

Kosovo officially remains a province of Serbia, but has been run by a U.N. mission and NATO peacekeepers after a 1999 air campaign by NATO drove out Serb forces who had been cracking down on independence-minded ethnic Albanians.

In Nis, Serbia's second-largest city, 5,000 extremists gathered midmorning on the main square, chanting "Slaughter, death to all" Kosovo Albanians, and "Let's all go to Kosovo!" From there, they headed toward a mosque, which they had set on fire earlier Thursday.

Crowds also protested in the city of Novi Sad, demolishing a local Islamic community headquarters and hurling stones at houses in a poor neighborhood believed to be occupied by Muslims.

Serbian officials tried to calm the surging nationalist passions.

"Our churches won't be repaired by the destruction of mosques," said Serbia's senior official for Kosovo, Nebojsa Covic. He was referring to reports that numerous Serbian Orthodox Churches were destroyed by ethnic Albanian rioters in Kosovo on Wednesday.

Serbian Prime Minister Vojislav Kostunica appealed Thursday against violence, adding that attacks against Muslims in Serbia could "attract terrorists from abroad."

But Kostunica, a moderate nationalist, described Wednesday's clashes in Kosovo as "an attempted pogrom" of Kosovo Serbs "which amounted to ethnic cleansing and a humanitarian catastrophe."

In Belgrade early Thursday, riot police guarding the U.S. Embassy used tear gas and stun grenades to disperse rock-hurling protesters, mostly drunk soccer fans, who overturned cars and garbage cans and destroyed buses.

Serb nationalists consider the United States the biggest ally of Kosovo's ethnic Albanians, who demand independence from Serbia, the dominant republic in the Serbia-Montenegro union.

Police said 24 officers were injured in overnight clashes in the capital, two of them seriously. At least 100 demonstrators also were hurt.

Protests — with crowds demanding a march toward Kosovo and chanting "Kosovo is Serbia" — continued in Belgrade and Nis later Thursday.

Several hundred protesters, mostly high school students, clashed with riot police in Belgrade's exclusive Dedinje district as they tried to march toward the Albanian embassy. Police used tear gas to fight off the stone-throwing crowd.

In Belgrade, a Kosovo Serb protester demanded urgent military action in the province, where ethnic Albanians represent an overwhelming majority.

"There is chaos in Kosovo," Ivan Markovic said. "This government must send its troops to Kosovo. The army and police are our only hope."