Feb. 21 (Bloomberg) -- Serbian rioters set the U.S. Embassy in Belgrade afire, leaving a charred body inside as thousands of people rallied in a government-backed protest of Kosovo's secession from the Balkan state.

Police didn't identify the body, and the U.S. State Department said it wasn't that of an American citizen. More than 100 people were injured in the riots, Zoran Alimpic, Belgrade's acting mayor, said by telephone.

Several thousand protesters broke from a crowd of about 150,000 people and breached the embassy compound at 7 p.m. local time. They set fires and began throwing objects from windows. Police stormed the embassy 10 minutes later, flushed them out and helped douse the fire.

Police then chased protesters down the street while firing tear gas. The mob also torched a guardhouse outside the British Embassy, set fire to a car outside the Canadian Embassy and attacked the Croatian Embassy, the B92 TV channel said.

Undersecretary of State for Political Affairs Nicholas Burns told Serbian government officials during the violence today that the U.S. would hold them ``personally responsible'' for the safety of American citizens in the embassy, according to State Department spokesman Sean McCormack.

The security ``was completely inadequate to the task,'' McCormack told reporters in Washington.

Security Council

The U.S. persuaded the United Nations Security Council to adopt a statement condemning the attacks in the ``strongest terms'' and reminding Serbia's government of its responsibility to safeguard international embassies. The Council's statement stressed the ``fundamental principle of the inviolability of diplomatic missions.''

Serbia reacted to Kosovo's declaration of independence on Feb. 17 by vowing to reassert authority over the breakaway province. The U.S., U.K. and Germany have recognized Kosovo's new status, while Russia condemned the move as a violation of international law.

Demonstrators also stormed and damaged Raiffeisen and Uni Kredit banks as well as a McDonald's restaurant in Slavija Square, B92 TV said. People were seen running from a department store with sporting goods, the Associated Press reported.

The State Department said the embassy compound was empty except for security personnel and Marine guards when the protesters attacked. The embassy sent home its employees at noon in anticipation of the demonstrations. The U.S. told citizens to avoid downtown Belgrade and issued an alert on travel to Serbia.

``The perimeter has been secured,'' McCormack told reporters in Washington late today. ``We are in control of the embassy compound itself.''

Role of Police

Zoran Zivkovic, a former Serbian prime minister, said local police guarding the U.S. Embassy ``acted as if someone told them to stay idle and tolerate looting and burning.''

``I am sure they were ordered to deal with the aftermath, not with protesters,'' Zivkovic said by telephone.

Kosovo is 90 percent ethnic Albanian. Serbs refused to give it up because it is considered the birthplace of their state and faith. The Serbian government had declared today a shortened workday to encourage turnout at the protest.

To contact the reporters on this story: Aleksandra Nenadovic in Belgrade through the Prague newsroom at anenadovic@bloomberg.net; Demian McLean in Washington at dmclean8@bloomberg.net.

Last Updated: February 21, 2008 19:48 EST