Mr Barak said he was speaking "with complete certainty" because he was the former head of the Israeli Army intelligence branch and a former member of the forum of intelligence service heads.

The Iranian Government announced on Thursday that it would try the 13 on charges of spying for Israel and the United States.

The head of the Iranian judiciary, Ayatollah Mohammad Yazdi, told worshippers in Tehran on Friday that the authorities were carefully investigating their activities. He confirmed that they could face the death penalty if convicted.

Criticism from the West

US Secretary of State Madeleine Albright described the arrests as "unacceptable". British Foreign Office Minister Geoff Hoon also expressed concern. He said Britain was consulting its EU partners on the issue and would be raising its concerns with the Iranian government.

Mr Barak said he had asked the United Nations General Secretary, Kofi Annan, to take urgent measures to obtain the release of the detainees.

But the English-language Tehran Times warned other countries not to interfere in the case.

"The US call for the release of the spies is flagrant interference in Iran's internal affairs," said the paper.

President Khatami: trying to build bridges with the US

It reminded Washington that one of Iran's preconditions for rapprochement after 20 years of frosty relations was "its pledge not to meddle in Iran's internal affairs"

The 13 were arrested in February and March in the southern province of Fars. Western governments learnt of the detentions, but remained silent in the hope that this would improve the chances of an early release.

There are 27,000 Jews in Iran, and Judaism is an official minority religion.

Some Western diplomats suspect that the arrests could be an attempt by hardline conservatives opposed to Iranian President Mohammed Khatami to prevent any improvement in Iranian-US relations.