His comments follow an announcement by the authorities in Belgrade that the war crimes tribunal in The Hague had no jurisdiction over the troubled province of Kosovo.

The envoy, David Scheffer was speaking at an international conference on war crimes in the Yugoslav capital, Belgrade attended by lawyers and prosecutors from across the country.

Also attending are speakers from Bosnia, Croatia, ethnic Albanians from Kosovo and Serbians.

He said the court had been established by the UN Security Council in 1993 in response to the carnage in the former Yugoslavia and no country had the right to refuse its jurisdiction.

"This is not a debatable issue," he said.

'Serious violations'

Mr Scheffer said there were reasons to believe that "serious violations of international law" were committed in Kosovo.

"In the UN Security Council there is unanimous consent of all its members that investigators of The Hague tribunal have full authority to do their job in Kosovo," he said.

UN War Crimes Tribunal Prosecutor Louise Arbour

On Wednesday the tribunal's Chief Prosecutor Louise Arbour and her team of investigators were told by the Belgrade government that they would not be allowed to visit Kosovo.

In protest Ms Arbour cancelled her planned attendance at the Belgrade meeting.

The government said Yugoslav forces had been engaged in a "legitimate repression" of a "separatist and terrorist" Albanian movement by government forces.

But the US envoy said government arguments "that this is strictly an internal armed conflict completely ignores the facts of what has occurred."

The tribunal's president, Gabrielle Kirk McDonald has also condemned the action as "a further example of the Federal Republic of Yugoslavia's disregard for the norms of the international community."

UN sanctions

The government has been threatened with UN sanctions if the authorities continue to defy their demands for unlimited access and their refusal has overshadowed the two day conference.

Three resolutions this year have called on the Yugoslav authorities to cooperate with the tribunal. Western countries are now likely to press for a fourth.

At the start of the conference Serbian lawyer, Milan Vujin, delivered a vigorous attack on the activities of he tribunal.

He said the body had been set up for political motives to punish Yugoslavia, and that many of its statutes contradict one another.

But the US envoy rejected the charge saying the integrity of its prosecutors and judges was unquestionable.