Air raid sirens sounded across Serbia to mark the 10th anniversary of the NATO bombing that ended Belgrade's rule in Kosovo.
Officials denounced the raids, which NATO carried out to force then-President Slobodan Milosevic to halt his onslaught against separatists in the former Serbian province.
"The attack on our country was an illegal act," Prime Minister Mirko Cvetkovic said on Tuesday. "Serbia cannot forget those tragic days."
Classes in Serbia's schools opened with a minute of silence for the victims. The government held a special session dedicated to the anniversary and ministers planned to lay wreaths at bombing sites throughout the country.
The ceremonies illustrate continued anti-Western sentiment in Serbia over the NATO air war, which forced the country to relinquish control over Kosovo to the United Nations and NATO.
Later yesterday, about 1,000 hard-liners chanted "We Want Guns" and booed the mention of NATO during a rally in downtown Belgrade.
Hundreds of riot police deployed nearby to prevent unrest similar to that which followed Kosovo's declaration of independence last year. In that violence, nationalists demolished the city center, and smashed and set fire to the US and other Western embassies.