The Federal Government has been accused of ignoring international human rights conventions by deciding to deport a Sydney Muslim Shia cleric.

Iranian-born Sheikh Mansour Leghaei, who has lived in Australia for the past 16 years, will be deported within six weeks because ASIO made an adverse security finding against him in 1997.

The United Nations advised the Government not to deport the sheikh because of claims he had been denied a fair hearing over the adverse security finding.

Dr Leghaei had asked Immigration Minister Chris Evans to use his ministerial power to allow him to stay in Australia.

Senator Evans said he carefully considered whether to stop the cleric being deported from Australia but declined to intervene in his case.

"The Department has spoken to him this morning and advised him that his wife and son have been granted visas on the basis of their long-term residence and their connection and integration in Australia," Senator Evans said.

"But because of the adverse security assessment on Dr Leghaei he will not be granted a visa and I will not intervene on his behalf."

Dr Leghaei's supporters say he is a leader of inter-faith relations between Muslims and Christians.

He has been fighting to get permanent residency for 13 years.

But standing in his way is the ASIO security assessment, which says he is a threat to national security and is suspected of "acts of foreign interference".

Under Australian law, ASIO is under no obligation to tell Dr Leghaei why it suspects him, so he has taken his case to the Immigration Review Tribunal, the Federal and High Courts.

The sheikh says he has never been told of the allegations contained in his ASIO file or been given the chance to respond to them.

"That is the mystery in this case, that you are thought to be a risk to national security, despite all the positive work that you have done here and despite all numerous letters of support," he said.

"It's not only local community, the wider community also knows me and respects all what I've done."

The sheikh's barristers have written to the United Nations claiming the Government's treatment of his case violates his human rights under international covenants that Australia has signed.

The co-director of Sydney University's Centre for international law, Ben Saul, is one of the barristers representing the sheikh.

Associate Professor Saul says the sheikh should be given a chance to answer the allegations against him.

"If there's evidence, all the sheikh asks is that evidence be provided to him so that he can challenge it," he said.

"How can a person get a fair trial? How can a person get a fair hearing unless they see at least some of the evidence against them? The sheikh's seen nothing.

"He's been denied an opportunity for a fair hearing in his national security deportation assessment.

"International human rights law requires that a person be given sufficient information or access to the evidence against them before they're deported on national security grounds.

"And at no time has the sheikh been able to see any of the evidence against him."

Today Associate Professor Saul produced copies of a letter the UN wrote to the Australian Government on April 21 asking it not to deport Dr Leghaei for at least a year, while it considered his case.

"If Australia proceeds to deport the sheikh it will be in direct contravention of its obligations under its international human rights treaties and in direct contravention of a specific order issued by the UN committee," he said.