Wellington, May 28 NZPA - A senior Australian politician's suggestion that Australian security services had forged foreign passports has credibility, according to a New Zealand academic.

But Waikato University senior lecturer Ron Smith, who specialises in international relations and security policy, said he'd be surprised if this country's Security Intelligence Service (SIS) used such tactics.

The SIS itself refused to comment on the issue, which caused a political storm across the Tasman this week.

"The New Zealand Security Intelligence Service has no comment to make on this matter. It is the service's long-standing position that it will not comment on security related matters," a spokesperson told NZPA.

Australian Prime Minister Kevin Rudd chastised the Opposition's foreign affairs spokeswoman Julie Bishop this week for putting national security at risk by her claims that Australia forges passports.

Dr Smith said the accusation that Ms Bishop had breached a long-standing convention with her remarks to journalists suggested the source of her information was Australian intelligence services.

"In a way if an Opposition spokesperson who had not received a briefing on this (intelligence) had said this, it would not be problematic," he told NZPA.

"I don't think there is any doubt this is the sort of thing intelligence services do."

Dr Smith said Ms Bishop was suggesting that the Australian government's protestations against Israel for passport forgery were hypocritical and designed to curry favour with Arab countries in order for Australia to get on the United Nations Security Council.

"Again that is what politicians do, that is the way countries behave. On the other hand, that convention about security is important so the perception that she has breached confidentiality damages the whole system which depends on that being strictly adhered to."

Dr Smith said he had no knowledge of either Australia or New Zealand intelligence services forging passports but "countries generally are doing this sort of thing".

Australia had an overseas intelligence bureau, but New Zealand engaged in less overseas intelligence.

"Our own SIS is ostensibly tasked for internal intelligence. We know they extend it to overseas, but I'd be surprised if they do very much, so I'd be surprised if they'd be involved in the sort of operation where this would even be plausible."

Ms Bishop made her comments following the Australian government's decision to expel an Israeli diplomat over the use of fraudulent Australian passports in the murder of a Hamas leader in Dubai in January.

Mr Rudd said: "There is a long-standing convention in Australian politics because of significant national security reasons neither side of politics speculates on, comments on the operation of our intelligence agencies.

"Today that convention has been breached and this is fundamentally contrary to Australia's national security interests."

Two men reported to be agents of Israel's Mossad service were caught and jailed for trying to illegally obtain New Zealand passports in 2004. A third suspected Mossad agent stole the identity of a tetraplegic Aucklander to fraudulently obtain another passport.