Serb TV showed images of the interrogation of the aid worker, named as Steve Pratt, 49.

Mr Pratt said he had used his position as a worker for the international aid organisation, Care, to gather intelligence about Kosovo and the effects of bombing.

He also apologised for activities which could have been detrimental to the country.

But the head of Care, Peter Bell, has said he does not believe Mr Pratt's statements.

Mr Bell called the confession bizarre, suggesting that it had been made under duress.

No sign of second detainee

Serbian television said Mr Pratt was part of a network of agents which had been smashed by the Yugoslav authorities.

It made no mention of Peter Wallace, who disappeared along with Mr Pratt on 31 March.

Mr Pratt bore no obvious signs of physical mistreatment and spoke calmly and clearly in English, with his words translated into Serbian. He was shown in profile and the television referred to him as "major".

Steve Pratt: No physical signs of ill-treatment

"When I came to Yugoslavia, I performed some intelligence tasks in this country by using the cover of Care Australia," Mr Pratt said.

"My concentration was on Kosovo and some effects of the bombing. I misused my Yugoslavian citizen staff for the acquisition of information.

"I realise that the damage was done this country by these actions, for which I am greatly sorry. I always did and still do condemn the bombing of this country."

Demands for release

Before the broadcast, the Australian Government had said it knew the two were being detained and called for their release.

Raja Jarrah, Care International UK: No reason to believe the two involved in anything illegal

A spokesman for Care said the organisation had no reason to believe that Mr Pratt was involved in intelligence work.

"We have had no official confirmation from the Yugoslav authorities on the grounds for his arrest or the grounds for these accusations," Raja Jarrah from Care International UK told the BBC.