Serb rioters enraged by Kosovo's secession stormed the US embassy in Belgrade and set it on fire, leaving one person dead and drawing swift condemnation from Washington and the UN Security Council.
The US State Department said the lack of protection for its mission, riot police were nowhere to be seen when the attack began on Thursday, was intolerable and demanded the Security Council respond.
"The members of the Security Council condemn in the strongest terms the mob attacks against embassies in Belgrade, which have resulted in damage to embassy premises and have endangered diplomatic personnel," the Security Council said in a unanimous statement.
Embarrassed, Serbia said it regretted what it called acts of isolated vandals who did not represent a nation which, while bitter at Kosovo's declaration of independence on Sunday, did not want further violence.
"The acts that were committed are absolutely unacceptable, absolutely regrettable," Foreign Minister Vuk Jeremic told Reuters in an interview. "They hurt Serbia's image abroad."
Germany, Croatia and Britain also said their missions were vandalised. Local media added Bosnia's and Turkey's to the list.
Some 200,000 people attended the state-backed rally. Jeremic said police were overwhelmed by what was Serbia's biggest march since protesters stormed the old Yugoslav parliament building in 2000 to oust nationalist leader Slobodan Milosevic.
But just a few score rioters, many wearing balaclavas, attacked the US embassy for the second time in a week, forcing their way in while police were nowhere to be seen.
One man climbed up and ripped the Stars and Stripes off its pole. Other people jumped up and down on the balcony, holding up a Serbian flag as the crowd below of about 1,000 people cheered them on, shouting "Serbia, Serbia".
Smoke billowed out of the embassy. Papers and chairs were thrown out of the windows, with doors wedged in the window frames and burning. American officials said only security personnel were at the embassy at the time, in a different area.
Riot police arrived later and fired teargas to disperse the crowds. A charred body was later found inside, probably of a protester; the embassy said its US staff were accounted for and Marines protecting it had not engaged in any fighting.
Hospital officials said around 150 people were injured in street clashes, including 30 police and some journalists.
At the United Nations, the statement by the 15-nation council recalled the inviolability of diplomatic missions but welcomed steps by Serbian authorities to restore order.
The council has been a battleground over Kosovo, with Russia refusing to accept Western moves to legitimise the mainly Albanian region's independence after nine years as a UN ward.
Serbia considers Kosovo its historic heartland and waged a diplomatic campaign against its secession on Sunday.
"As long as we live, Kosovo is Serbia," Prime Minister Vojislav Kostunica had told the state rally, where Serbs of all ages listened to speeches and melancholic patriotic songs about Kosovo, seen as the birthplace of a proud medieval kingdom.
Washington said Kostunica later pledged there would be no repeat of the attacks, but an analyst said tension would remain.
"Additional acts of what is effectively political vandalism can be expected," said Jon Levy of the Europe and Eurasia think tank.
The Belgrade rioters also vandalised shops and banks, especially Western ones, leaving a trail of smashed glass and debris. There was some looting.