PRISTINA, Kosovo — Well-organized Serb gangs torched buildings Tuesday along the border between Serbia and Kosovo in a defiant rejection of the breakaway province's declaration of independence.

Huge flames and walls of black smoke engulfed border posts, U.N. police and customs offices in the most serious violence to date over Kosovo's unilateral split from Serbia, declared by the ethnic Albanian government Sunday.

United Nations police, who have helped administer Kosovo for the past nine years, were forced to flee, and NATO troops rushed to the scene to restore order.

The Serbian militants appeared to be enforcing their own partition of Northern Kosovo, where many Serbs live, from the rest of the Albanian-dominated province by erasing the more official borders.

Although Serbian Prime Minister Vojislav Kostunica on Monday called for restraint from Serbs, his government Tuesday seemed to encourage the groups wreaking havoc along the frontier.

Slobodan Samardzic, Serbia's minister for Kosovo, said the central government was not behind the gangs' vandalism. But, he said, Serbia fully intends to take over customs functions in Northern Kosovo.

"Today's action is in accordance with general policy of the government to take over customs policy wherever it can in Kosovo, as well as all other policies, all other responsibilities. That is simply a process that is not going to be stopped," he told Belgrade's B92 television.

"We saved the face. We saved a part of Kosovo," Samardzic said. "Serbia will never recognize the independence of Kosovo."

He denied Serbia was attempting to slice off Northern Kosovo. But, he said, "We preserved a part of Kosovo."

Recognition of an independent Kosovo, he said, was "total madness."

The U.S. and many European countries have recognized the new country, but Russia, Serbia and others say Kosovo's revolt is illegal.

Kosovo Prime Minister Hashim Thaci, asked about Tuesday's violence, said Kosovo Albanians would not be provoked.

"Everything is under the control of the NATO authorities, Kosovo police and the United Nations, and no isolated incident will undermine Kosovo's independence celebrations," he told a news conference with EU foreign affairs chief Javier Solana.

Solana arrived in town to offer EU support. The EU will take over from the U.N. in the next four months as supervisor of Kosovo's fledgling institutions. The U.N. mission has governed Kosovo since 1999, when NATO bombing halted Serbian attacks on ethnic Albanian separatists.