You just can't take that sort of action into your own hands on the high seas

Federal Customs Minister Chris Ellison

The group described itself as a "non-profit, non-political, non-racial organisation interested only in the future" of Australia.

But Immigration Minister Philip Ruddock said the advert was "highly irresponsible".

He said federal police were investigating.

Detention camps

However, so far the group has not been traced. E-mails sent to the address on the advert were returned, though the ad also gave a reply box address at the West Australian newspaper.

The advert, published on Thursday, said: "Patrols will be undertaken in international waters without the constraints of political correctness."

Asylum seekers are detained in camps

Australia accepts about 10,000 refugees a year resettled under formal United Nations programmes. But the government has taken a tough stance against illegal immigrants, whom it calls "queue jumpers".

In the last year more than 50 boats have been intercepted carrying 4,000 asylum seekers, mostly from the Middle East and Afghanistan. The latest, carrying 113 illegal immigrants and five Indonesian crew, arrived last week.

Illegal immigrants are detained in remote outback camps while their asylum claims are being processed.

Mr Ruddock said the government was already doing everything it could to ensure boat people, most of whom seek asylum upon arrival, were intercepted before they reached shore.

"To believe that you could do something more, and the sorts of advertisements that we're seeing suggest that there would be some form of armed response, is highly irresponsible," he said.

"It would be a breach of our law to be involved in such activities, it would be a breach of people's entitlements on the high seas, to try and interdict them with force."

Piracy

Federal Customs Minister Chris Ellison said vigilante groups risked "the full consequence of the law."

"There are international laws that apply in relation to piracy and we've signed those treaties and you just can't take that sort of action into your own hands on the high seas."

Australia has been criticised recently by international human rights groups over its mandatory detention of asylum seekers, but polls have suggested little sympathy among the public.

A recent poll for Channel Nine's Sunday programme showed 78% public support for the government's hardline stance, which is also backed by the Labour opposition.