Serbians have sounded air-raid sirens and rung church bells in remembrance of people killed in Nato's bombing against Serbia 10 years ago.
The military alliance ordered the 11-week bombing on March 24 1999 after Slobodan Milosevic, the then Serbian president, refused to sign an internationally-brokered peace plan for Kosovo.
Nato's forces sought to force Serbia out of the province of Kosovo, where Serbians were being accused of persecuting the Albanian majority.
Boris Tadic, Serbia's president, in a speech on the eve of the anniversary before the UN Security Council in New York, described Nato's intervention as a "tragic military campaign".
"The lesson for Serbia is that it must not get into a situation in which its citizens are punished and killed ever again," he said.
"Some 2,500 civilians were killed, among them 89 children, while 12,500 were injured," said Tadic, whose governing Democratic Party opposes Kosovo's independence.
Human Rights Watch, a Washington-based human rights group, put the civilian death toll from the bombing campaign, which lasted 78 days, at about 500.
Serbia estimates that the campaign cost $30bn from direct damage alone.
Kosovo Albanians widely believe that the bombing of the forces helped them realise their independence.
At least 15,000 Nato-led peacekeepers remain in Kosovo, which 56 nations recognise after its ethnic Albanian-dominated parliament declared unilateral independence from Serbia in February 2008.