The man was gunned down in Mother Teresa Street - one of the city centre's busiest pedestrian thoroughfares - while taking a walk after dinner. It was his first day in the job.

BBC News' David Campanale: Shooting coincides with Kofi Annan's visit

The shooting came two days before the visit of the UN secretary-general, his first to Kosovo since it was effectively put under international control.

A UN spokesman said the victim had apparently been assaulted before being shot.

It turned he was Bulgarian national, wearing civilian clothes and carrying a US driving licence.

An international police officer said the victim had been asked for the time by a group of teen-agers, and he responded in Serbian.

The victim had arrived earlier in the day at the start of a civilian assignment with the UN mission, which alongside the Nato-led Kosovo Force (Kfor) is responsible for policing the province.

Annan tour

The victim "was a middle-aged, adult male, possibly of Albanian descent" - UN spokesman

Mr Annan is currently on a tour of the region and met Bosnia's multi-ethnic presidency in Sarajevo on Monday.

He was briefed on the progress the country has made in building peace and restoring civil society since the 1992-1995 war.

At a ceremony honouring all those who served as UN peacekeepers during the conflict, Mr Annan apologised for the world's failure to end the war in Bosnia sooner.

"No one laments more than we the failure of the international community to take decisive action to halt the suffering and end a war that had produced so many victims," he said. "The tragedy of Srebrenica will haunt our history forever."

For their part, Bosnia's three leaders gave their backing to an initiative to build a memorial to all UN personnel who lost their lives during the peacekeeping mission.

Tensions in Serbia

But it is the humanitarian challenge in Serbia which now commands the attention of international diplomacy.

With winter approaching, the European Union has approved a plan to provide heating oil to two towns controlled by the opposition in Serbia, whose power grid was badly damaged by Nato bombing earlier this year.

Nis and Pirot are to receive the fuel in spite of the current oil embargo on Yugoslavia.

But a number of opposition leaders have objected that future aid is being made dependent not only on a restoration of democracy in Serbia, but to the handing over of war crimes suspects.

The BBC Belgrade correspondent says the War Crimes Tribunal for the former Yugoslavia is seen by many as primarily set up to prosecute Serbs.

A rare appearance by Mr Milosevic

The European plan has also been opposed by the United States, which fears it could help Mr Milosevic.

He made a speech fiercely denouncing his domestic opponents, in what was his first direct reaction to recent street protests calling for his resignation.

He said the opposition wanted to turn Serbia into a pro-Western colony.

"They are cowards and bootlickers, who are threatening to destroy what we have defended from Nato," Mr Milosevic said.