Rioting engulfed Kosovo (searchWednesday after ethnic Albanians blamed Serbs for the drowning of two boys. The violence left eight dead and nearly 300 injured in one of the bloodiest days since the end of the Kosovo war in 1999.

Melees broke out in every major city in the province as well as several enclaves where Serbs have eked out a sheltered existence since the war ended. Serb homes, churches and cars were set on fire as ethnic Albanians rampaged in revenge.

Most of the casualties occurred where the violence erupted — the ethnically divided city of Kosovska Mitrovica (searchas the two sides threw rocks and charged at each other and then opened fire with guns.

The breakdown in order illustrated the failure of U.N. and NATO (searchefforts to snuff out ethnic hatreds and set the U.N.-run province on the path of reconciliation.

Late Wednesday, armored personnel carriers and police in riot gear were placed in and around the U.N. headquarters in Kosovo's provincial capital of Pristina (search) to prevent attacks.

The dead included six ethnic Albanians and two Serbs, said Derek Chappell, the chief U.N. police spokesman. One of the ethnic Albanians died in the western town of Pec, Chapell said. A U.N. police officer shot the ethnic Albanian who was attempting to hit the officer with a brick, Chappell said.

In the ethnic Albanian side of Kosovska Mitrovica, hospital workers counted more than 200 hurt, including several who were shot. Floors were stained with blood, and doctors appealed for blood donations. On the Serb side, Dr. Milan Ivanovic said 80 Serbs were wounded.

The clashes in Kosovska Mitrovica erupted after reports that Serbs in a nearby village set a dog on a group of ethnic Albanian boys, sending three of them fleeing into an icy river, where two drowned and a third was missing.

After authorities recovered two bodies, ethnic Albanians and Serbs gathered near a bridge over the Ibar River that separates Kosovska Mitrovica, long the flashpoint of tensions. The two sides traded insults, threw rocks and charged each other several times before gunfire rang out and rioters set U.N. police cars ablaze.

Protests also swept Belgrade, the capital of Serbia-Montenegro. Demonstrators set the city's 17th century mosque on fire after clashing with police trying to guard the building. They demanded that the government act to protect their Orthodox Christian kin in Kosovo from attacks by the province's predominantly Muslim ethnic Albanians.

Another mosque in the southern city of Nis was also set ablaze. Mobs roamed the streets of Belgrade into the early morning hours Thursday.

In a melee near Pristina, hundreds of ethnic Albanians broke through barricades erected by U.N. police and NATO-led peacekeepers to march on the Serb village of Caglavica. Hand grenades were thrown and Serb houses were set on fire, said Angela Joseph, a U.N. police spokeswoman.

In Pristina itself, U.N. cars also were torched. In the nearby city of Kosovo Polje, dozens of Serb houses and a hospital were set ablaze, ethnic Albanians appeared to be in control on the streets.

Riots also were reported in the western city of Pec, crowds clashed with peacekeepers and police in the town of Gracanica, and cars were destroyed in the city of Gnjilane.

U.N. Secretary-General Kofi Annan condemned the violence, saying it "jeopardizes the stability of Kosovo and the security of all its people," according to a U.N. spokesman.

The United States called on Kosovo's political leaders to use their influence to restore calm. "The escalating violence must end," the State Department said. "It threatens the process of democratization and reconciliation in Kosovo, and threatens the very future of Kosovo."

Kosovo is administered by the United Nations but remains part of Serbia-Montenegro, the successor state to Yugoslavia.

Serbs see Kosovo as their ancient homeland. Ethnic Albanians want independence from Serbia-Montenegro. Hatreds between the two sides continue to boil over into violence, with each act of bloodshed leading to revenge from the other side.

Wednesday's violence was the worst since February 2001, when ethnic Albanian terrorists blew up a bus carrying Serbs, killing 11 and injuring 40.

Other recent ethnic bloodshed also targeted Serbs, including one incident in which three members of a family were axed to death in their home and another in which two teenagers were shot to death while swimming in a lake.

Fewer than half of the more than 50,000 NATO troops sent to Kosovo remain. he violence is a blow to hopes by Washington and its allies that troops in Kosovo and elsewhere in the Balkans can be redeployed to Iraq, Afghanistan and other areas.

The Kosovo war ended in 1999 after a NATO air campaign drove Serb-dominated troops loyal to former Yugoslav President Slobodan Milosevic out of the province and stopped a crackdown on the ethnic Albanian majority. An estimated 10,000 people died in the war, most of them ethnic Albanians.