Kosovo Serbs were shocked by the killing

He is the highest-ranking Serbian politician to visit the province since the United Nations took over its administration four years ago.

The Serbian Government declared Friday a day of national mourning for the youths, whose killings have outraged Kosovo's remaining Serbs.

On Thursday, the UN appointed a special prosecutor to investigate Wednesday's attack, and a major police operation is under way.

Before leaving Belgrade, Mr Zivkovic said that not a single perpetrator of an act of violence against non-Albanians in Kosovo had been found, let alone punished.

Serbs should gather enough strength not to leave Kosovo Serbian PM Zoran Zivkovic

Nato-led peacekeepers put a security cordon round the village of Gorazdevac, before he and Deputy Prime Minister Nebojsa Covic arrived for the funerals.

Hundreds of local Serbs also attended.

Ivan Jovovic, 19, and Pantelija Dakic, 13, were killed and four others injured by automatic gunfire while swimming in a river near the village, a Serb enclave.

No-one has admitted responsibility.

Serbs blame pro-independence ethnic Albanians for a recent wave of violence, including the killing of a Serb family in June, and a series of smaller attacks.

Protests

The incidents come ahead of planned talks between ethnic Albanian officials and the Serbian authorities - the first since the end of the 1999 conflict.

After Wednesday's shooting, local Serbs blocked a key road in the village of Osojane, western Kosovo.

I promise to do everything to bring the perpetrators to justice Harri Holkeri

There have also been reports that a grenade was thrown at the house of an ethnic Albanian in the divided northern town of Mitrovica.

Protests continued on Thursday.

Between 80,000 and 120,000 Serbs are estimated to remain in Kosovo, in enclaves protected by Nato peacekeepers - roughly a third of the pre-war figures.

Mr Zivkovic said at the funerals: "Serbs should gather enough strength not to leave Kosovo."

Wednesday's attack occurred hours after Mr Holkeri, a former Finnish prime minister, arrived on his first visit to the region following his appointment.

"I am extending my deepest sympathies to the families of the victims of this senseless violence, and I promise to do everything to bring the perpetrators to justice," he said after a meeting on Friday in Belgrade with Mr Zivkovic.