Australain Foreign Minister Alexander Downer said the men were completely innocent and described Saturday's verdict as "incomprehensible", "outrageous" and "deeply distressing".

The three men - two Australians and one Yugoslav - had been working in Yugoslavia for the aid agency, Care Australia (CARE), at the time of their arrest two months ago.

BBC's Jim Fish: The severity of the sentences has shocked many people

Observers were barred from the trial, which started on Wednesday, but journalists were allowed in to hear the verdicts of the five-man military panel.

CARE worker Steven Pratt was sentenced to 12 years, and Peter Wallace was handed a four-year term.

A Yugoslav employee of the organisation, Branko Jelen, received a six-year term.

The BBC's Red Harrison: "The government is trying to persuade Belgrade to release them"

The defendants have been given three days to appeal.

When the sentences were read out in court, Jelen's mother said: "Why did you do this to my son? He's not guilty."

Care Australia spokesman Brian Doolan said the verdict had serious implications for all aid workers in and around Kosovo.

"That means of course that there are some 50,000 Serbian refugees who are currently reliant on Care for the provision of food and fuel who may no longer be able to access that food and fuel through Care," he said.

The trial went ahead despite appeals from UN Secretary-General Kofi Annan and South African President Nelson Mandela.

Steven Pratt pictured with his wife

Several visits were also made by the CARE's head and former Australian prime minister, Malcolm Fraser.

Steve Pratt was charged with organising an espionage network and his colleagues with helping him. They denied the charges.

The two Australians were arrested as they tried to leave Serbia for neighbouring Croatia.

They were carrying files and computers which the Yugoslav authorities said contained sensitive information intended to be passed to Nato.

Air-dropped food

Despite the decision, an international aid organisation has announced that it is to begin dropping food to displaced people inside Kosovo within the next few days.

The International Rescue Committee announced in New York that it would fly two chartered Russian planes from Italy and drop enough food to feed 15,000 people a day.