The attack on the embassy came after hundreds of protesters, watched passively by police, peeled away from the main rally to invade the building in the centre of the capital, using sticks and metal bars.

Witnesses described how the doors to the unprotected embassy — closed after being attacked earlier this week — were knocked in and used to start a fire in an office while demonstrators cheered. Firefighters swiftly put out the flames.

A charred body was later found in the embassy. "It was found at the part of the building set on fire by the protesters," an embassy spokeswoman, Rian Harris, said. She said all embassy employees were accounted for.

Belgrade's Pink TV said the body appeared to be that of a rioter. The British embassy also came under attack.

Groups of protesters also broke into a McDonald's restaurant and other western-owned businesses in Belgrade.

The rally was the largest since demonstrators filled the streets in 1999 to protest at Nato bombing and stormed the parliament building in October 2000 to oust the nationalist autocrat Slobodan Milosevic.

Papers and chairs were thrown out of the embassy's windows, while one protester climbed up to the first floor of the building, ripped the US flag off its pole and briefly put up a Serbian flag in its place.  The attack on the building and the  Croatian embassy followed claims by European defence chiefs meeting in Slovenia that security in the Balkans was "under control".

Schools closed

The rally came after the government ordered Serbian schools closed for the day and the state rail company made free trains available to bring protesters to the capital.

Organisers say the rally was intended to demonstrate Serbia's commitment to holding on to the former province of two million people.