MANSOUR Leghaei, the Iranian cleric twice declared a security threat by ASIO, has been given 28 days to leave the country after an immigration appeals tribunal rejected his final application to remain in Australia.

For more than a decade, Dr Leghaei has been contesting in the courts two adverse security assessments issued by ASIO, which it is understood believes the cleric is an Iranian operative. Dr Leghaei's battle to remain in Australia has won high-profile backing, with Attorney-General Robert McClelland writing two character references for the Sydney-based sheik, one of which challenged ASIO's findings.

But on Friday, the Migration Review Tribunal upheld a decision by the Immigration Department denying the sheik a residency visa.

As a result, the department has cancelled Dr Leghaei's bridging visa, giving him 28 days to leave.

A spokesman for Immigration Minister Chris Evans said ASIO had indicated it had no objection to Dr Leghaei remaining at large in the community while he finalised his affairs. "Dr Leghaei should now make arrangements to depart Australia. The department will seek to engage with Dr Leghaei in the coming weeks to facilitate his departure," he said.

The spokesman said the tribunal's decision also applied to Dr Leghaei's wife and one of his adult children, meaning their bridging visas would also be cancelled in 28 days.

At least one of Dr Leghaei's children was born in Australia.

During his hearing, the sheik argued little weight should be given to ASIO's assessment as the agency had refused to provide the reasons underpinning it.

But the tribunal ruled that, while sympathetic to Dr Leghaei's predicament, it lacked the authority to examine or overrule ASIO's judgment.

Mr McClelland wrote a reference for Dr Leghaei in 1997 while an opposition backbencher. He described the sheik as an asset to the Australian and Muslim communities.

"I was most surprised to learn that Sheik Leghaei's application had been rejected on the failure to satisfy part 4002 of Schedule 4 of the Migration Regulations, that is the public-interest criteria," Mr McClelland wrote.

But ASIO, which reports to Mr McClelland as Attorney-General, has taken a different view for more than a decade.

The Australian understands the agency still considers Dr Leghaei a security threat and has refused to undertake another assessment of him. Aside from his links with Iran, it is understood ASIO has concerns about Dr Leghaei's alleged knowledge of Ahlul Bait, a French terrorist organisation.

Dr Leghaei has repeatedly denied he has been a spy for Iran or is a threat to security. But his 1997 residency application was denied on public-interest grounds after ASIO found against him, and in 2002 the agency formally issued an adverse security assessment.

In 2004, a second adverse security assessment was handed down. Despite the concerns, Dr Leghaei has lived freely since arriving in Australia in 1994. At one point he did not even have a valid visa, meaning that in addition to being a security threat, he was living unlawfully in Australia.

Dr Leghaei could not be contacted for comment.