US Embassy in Belgrade Attacked
Several hundred protesters have attacked and broken into the US embassy in the Serbian capital Belgrade, setting fire to part of it.
The embassy was closed and unprotected at the time. Reports say the Croatian and UK embassies were also attacked.
The violence follows a peaceful protest by at least 150,000 people outside the main parliament building against Kosovo's declaration of independence.
The US, the UK, Germany and Italy are among those to have recognised Kosovo.
The attacks overshadowed the earlier peaceful demonstration, when Prime Minister Vojislav Kostunica addressed protesters in the main square, saying Kosovo would always be Serbian.
Most Serbs consider Kosovo their religious and cultural heartland.
Prayers
US state department spokesman Sean McCormack said a number of Serbians had penetrated the embassy compound, and urged the authorities there to take control of the situation.
A blaze broke out in several rooms inside the compound.
One protester climbed onto the first floor and ripped the US flag from its pole. Riot police backed by armoured cars fired tear gas at the protesters.
Correspondents in Belgrade say the atmosphere on the streets remains volatile.
Earlier, protester Jelena Subin told the BBC it felt as if there were a million people at the Belgrade rally.
"There is a great feeling of sadness, not anger. We want it to be a peaceful protest. We want to show the world that Kosovo belongs to Serbia," she said.
Mr Kostunica addressed the crowds from a large stage, draped in two huge Serbian flags and with a banner reading "Kosovo is Serbia" at the back.
"As long as we live, Kosovo is Serbia," he said to cheers and applause. "Kosovo belongs to the Serbian people."
"We'll never give up Kosovo, never!" the crowd responded.
"Is there any other nation on Earth from whom [the great powers] are demanding that they give up their identity, to give up our brothers in Kosovo?" he added.
Ultra-nationalist leader Tomislav Nikolic accused the US and EU of trying to steal Kosovo.
"We will not rest until Kosovo is again under Serbia's control," he said.
"Hitler could not take it away from us, and neither will today's [Western powers]."
Other speakers included Australian Open tennis champion Novak Djokovic, who addressed the crowd by video link.
After the speeches, the crowd marched to the city's biggest church, the Temple of Saint Sava.
Border protest
There was thick, black smoke billowing from the crossing point at Merdare, 50km (30 miles) north-east of Kosovo's capital Pristina.
Serbs waved large tricolour Serbian flags, chanted "Kosovo is Serbia" and tried to cross the border.
"We are here in support of the Serbs who still live in Kosovo," Dejan Milosevic, one of the organisers, told the Associated Press news agency.
The Kosovo police, backed by Czech troops from the Nato-led peacekeeping force, put a steel barrier across the road and were able to hold their line.
The Serbs have now pulled back and ended their protest.
Protest rallies were also held in the Bosnian Serb republic (Republika Srpska). There were unconfirmed reports of injuries as several hundred protesters clashed with police outside the US consulate in Banja Luka.
In the coming weeks, an almost 2,000-strong EU mission will be deployed to help the country develop its police force and judiciary.