Solemn ceremonies were held at Belgrade monuments to children and journalists killed in the NATO sorties as the sirens were sounded across the ex-Yugoslav republic for 60 seconds from midday (1200 CET).

Ministers gathered at the same time to lay wreaths at spots where people were killed during the air war -- at the time the biggest military operation in NATO history.

"The attack on our country was illegal, contrary to international law, without a decision by the United Nations" Security Council, Prime Minister Mirko Cvetkovic told a special commemorative sitting of his cabinet.

"The air strikes have not solved problems in Kosovo, and did not help to bring peace and the rule of law.

"They resulted in ethnic cleansing and gross violations of human rights, international standards and fresh tensions," he said, after schools held a minute's silence before class.

Kosovo leaders said however the NATO bombing stopped Serbian abuses in their breakaway territory and was a decisive step towards saving and freeing its people.

"The 78 days of strikes saved the people of Kosovo from planned extermination, a scenario which was prepared coldly by the highest Serb political and academic circles," Kosovo President Fatmir Sejdiu said.

Kosovo Prime Minister Hashim Thaci described the bombing as "a big historic event for Kosovo and the democratic world."

"The successful completion of the campaign of intervention by NATO opened a new chapter in the history of Kosovo, a chapter of freedom," said Thaci.