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.

The trial verdict was announced as

• signs emerged in Belgrade of a new attitude to the peace negotiations on ending the Kosovo crisis
• an aid agency said it was planning to make air drops to displaced people within the Serbian province for the first time.

International observers had been barred from the aid workers' trial, which began on Wednesday.

However 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.

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

The defendants have been given three days to appeal.

The trial went forward despite appeals from UN Secretary-General Kofi Annan and South African President Nelson Mandela, and several visits by the agency'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.