Key Points:

The Prime Minister is defending the decision to hold the review of high profile refugee Ahmed Zaoui's security risk certificate behind closed doors.

A four-week hearing into the Security Intelligence Service (SIS) assessment that the once-elected Algerian MP posed a security risk to New Zealand began in Auckland today, the first of what could be three hearings into the assessment.

The hearing before the Inspector General of Intelligence and Security, Justice Paul Neazor, is not open to the public, and the fact that the SIS in reaching its decision made use of classified material means that Mr Zaoui cannot fully view what the accusations against him are and who made them.

About 25 people, mostly from Amnesty International, staged a mainly silent protest outside the hearing before Mr Zaoui walked in.

They included a woman locked in a cage wearing orange overalls and others who were blindfolded and gagged that carried placards "secret evidence", "secret sources" and "secret hearing".

Prime Minister Helen Clark said an open hearing would not have been appropriate.

"It's not a court. It is a review of a security risk certificate," she said today.

"Obviously it involves the use of classified information and that is properly done outside what would be the procedures of a court."

Green Party human rights spokesman Keith Locke disagreed with Miss Clark's claim.

"The previous judgements of the Court of Appeal and the High Court make clear that Mr Zaoui should be subject to a proper legal process," he said.

"It is simply not a fair process to hide behind closed doors the legal jousting over the non-classified information -- which is all the hearing that began today is considering."

Amnesty International New Zealand refugee co-ordinator Margaret Taylor said human rights had been denigrated and denied during the war on terror under the excuse of security.

"The best form of security you can guarantee is when you have a security with basic human rights honoured and respected because that's the most lasting form of security.

"In Canada and also in the European Court of Human Rights they've done cases like this before and they've suggested that the best practice is to go forward with security cleared counsel and also in-camera proceedings.

"We would have been very happy as a human rights organisation if that had been the process but it's not."

Wearing a black coat and a black and grey scarf, Mr Zaoui was smiling as he entered the hearing and still looked in a good mood when he departed about 4.50pm today.

Mr Zaoui's lawyer Deborah Manning said before the hearing began this morning that the process was not a common one.

"It is very difficult of course to prepare for any hearing when information is secret so I don't think anyone's under any illusion that this is a normal fair hearing because it is based on secrecy."

There are three possible hearings into the security risk certificate, and two special advocates, Stuart Grieve QC and Chris Morris, have been appointed to look at classified material on Mr Zaoui's behalf.

Mr Grieve was allowed to make summaries of the classified material but was unable to tell them of all the details, including who the sources were that accused him of being linked to terrorist organisations in Algeria.

The hearing which began today will include several witnesses testifying about Mr Zaoui's character, after which further examination of classified material by Mr Grieve is possible.

A second hearing which considers aspects of classified material which Mr Grieve can pass on to Mr Zaoui and Ms Manning can then be held, at which Mr Zaoui and Ms Manning can be present.

After that, a third hearing which reviews classified material, at which only Mr Grieve can be present on Mr Zaoui's behalf, is expected.

Mr Locke said the special advocate process was questionable.

"Any rebuttal of the SIS's classified information is up to the two special advocates, Stuart Grieve QC and Chris Morris -- who are not allowed to mention anything about the classified information to the Zaoui team.

"Mr Zaoui was not even able to appoint the two Special Advocates. This was done by the Inspector General of Intelligence and Security, Paul Neazor, the man checking the validity of the security risk certificate.

"The way the hearing is proceeding undermines long-established principles of due process in our legal system."

Ms Manning said she hoped a decision would be made by the end of the year.

Mr Zaoui was democratically elected to represent the Algerian Islamic Front for Salvation (FIS) in December 1991, but the new government was overthrown in a military coup in January 1992 and he fled to Europe.

He has been accused of being associated with the militant Armed Islamic Group (GIA), but has denied any such involvement.

Mr Zaoui arrived in New Zealand in December 2002 and sought refugee status, saying he would be tortured or killed if he went back to Algeria, but spent almost two years in prison waiting for his case to be decided as he fought the security risk certificate.

Mr Zaoui was declared a genuine refugee in August 2003 by the Refugee Status Appeals Authority and released on bail in December 2004 where he has lived with the Catholic community in Auckland in the Dominican Priory.