The United States bluntly warned Serbia against inciting violence after an angry mob protesting the independence of the former Serbian province of Kosovo stormed and set fire to the U.S. Embassy in Belgrade on Thursday.

The attack played out live on television screens around the world and the Bush administration reacted with unusual sharpness, denouncing Serb authorities for failing to protect the compound from rioters who torched part of its main office building, causing undetermined damage and possibly the death of one person whose charred body was later found.

"Our embassy was attacked by thugs," White House press secretary Dana Perino told reporters aboard Air Force One as President Bush and Secretary of State Condoleezza Rice returned from a trip to Africa. "We have made known to the Serbian government our concern and displeasure that their police force did not prevent this incident."

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From the plane, Rice received updates as the assault unfolded and ordered the third-ranking U.S. diplomat, Nicholas Burns, to tell the Serbs that the attack was unacceptable, that their protection of the embassy was sorely lacking and that they must stop anything that might incite violent protests over the U.S. recognition of Kosovo's independence.

"The message was very clear: that the situation was intolerable, that they needed to act immediately to provide adequate security forces to ensure that our embassy compound and our personnel were not under attack," State Department spokesman Sean McCormack told reporters in Washington. "That is an international obligation that they must meet."

In stern phone calls to Serbian Prime Minister Vojislav Kostunica and Foreign Minister Vuk Jeremic, Burns "made it very clear that we would hold the Serbian government personally responsible for the safety and well-being of our embassy employees," he said.

Burns also told them that "the security that was provided was completely inadequate to the task" and "that we did not expect a repeat of the situation in the future," McCormack said, adding that the United States would seek U.N. Security Council action to condemn the attack.

The two men assured Burns that similar incidents would not be repeated but shortly afterward a top adviser to Kostunica's adviser, Branislav Ristivojevic, sharply criticized a U.S. demand for Security Council action, saying the United States was the one "violating international law" by recognizing Kosovo's independence over Serb and Russian objections.

"The United States, not Serbia, is brutally violating international order, and that is the issue that the Security Council should take up," he said.

Later Thursday, the Security Council strongly condemned the attacks on the embassies in the Serbian capital, saying host governments like Belgrade must honor their obligation to protect diplomatic premises.

The council unanimously condemned "in the strongest terms the mob attacks against embassies in Belgrade" and said that it welcomed "the steps taken by the Serbian authorities to restore order and protect diplomatic property and personnel, according to a statement read by the current council president, Panama's U.N. Ambassador Ricardo Arias.

Concerns that Serb politicians are encouraging mob violence, State Department spokesman McCormack said that had to stop.

"They have a responsibility to ensure that there is not, on the part of their ministers and their officials, an incitement to violence," he said. "That has to cease. There cannot be incitement to violence."

"It's very clear that there are differences with respect to the action that we took to recognize Kosovo and the actions that others have taken to recognize Kosovo," McCormack said. "We can talk about that, but none of those disagreements are an excuse or a justification to incite violence."

But he did not draw a direct link between the alleged incitement and the attack on the Belgrade embassy in which masked men smashed their way inside the compound's chancery building, tore down the U.S. flag and tried to throw furniture from an office.

They set fire to the office and flames shot up the side of the building. Police reinforcements and fire fighters did not arrive until about 45 minutes after the blaze broke out.

It was the first direct attack on a U.S. embassy since Sept. 12, 2006, when Syrian security guards stopped an attempt to blow up the compound, although last month the U.S. Embassy in Chad was evacuated after it was hit by indiscriminate fire. The last time a mob broke into one was the Iranians' seizure of the U.S. Embassy on Nov. 4, 1979, taking the American staffers hostage.