Several hundred Serbian army reservists hurled stones at police and NATO-led peacekeepers Thursday as they crossed into Kosovo during a clash at a border checkpoint.

The demonstrators — most wearing their uniforms and chanting "Kosovo is ours! Kosovo is Serbia!" — threw rocks and burned tires to create a billowing smoke screen before surging past the checkpoint in Merdare, about 30 miles northeast of Kosovo's capital, Pristina.

U.N. police said the demonstrators, all army veterans who fought on the Serbian side in Kosovo's 1998-99 war, arrived from the Serbian town of Kursumlija in buses and brought a bulldozer.

An Associated Press reporter at the scene saw riot police with shields and batons erecting a large steel barrier across the road in an attempt to keep them from getting deeper into Kosovo.

APTN video from Mitrovica shows demonstrators carrying signs depicting President Bush and reading: "Wanted: For Murder of International Law."

Several hundred Czech troops from the NATO-led peacekeeping force deployed to the site with armored personnel carriers, and NATO helicopters hovered overhead.

"We are here in support of the Serbs who still live in Kosovo," said Dejan Milosevic, one of the organizers. "We want to tell them that we will not let Kosovo be taken away. We will fight to our last breath."

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Serbs angry at Kosovo's independence declaration set fire to another border checkpoint earlier this week.

Tensions have remained high among Serbs in both Kosovo and Serbia, where Kosovo — home to dozens of important Serbian Orthodox churches and monasteries — is considered sacred territory.

But Rada Trajkovic, a Kosovo Serb leader, on Thursday called on Serbian Prime Minister Vojislav Kostunica to fire his minister for Kosovo, Slobodan Samardzic, for encouraging violent protests.

"Serbs from the north have brought other Serbs in Kosovo in a position to fear for their children and their lives, which is a very painful feeling — the fear of what your own people might do," the independent Serbian news agency FoNet quoted Trajkovic as saying.