Mr Fraser says the apprehension of the vessel on which they were travelling in international waters and their transfer to an Australian customs vessel was ''in breach of international law'', and he is unsure how else to describe it, other than as an act of piracy.

His remarks came as the fate of the asylum seekers, who are being detained on an Australian customs vessel on the high seas remains uncertain as their lawyers negotiate with the government on when they will be able to speak to their clients.

Amid speculation that they will be taken to the Nauru detention centre, Prime Minister Tony Abbott and Immigration Minister Scott Morrison refused to reveal where the boat is holding the asylum seekers or where they will be sent.

Revealing only that the asylum seekers, including about 40 children, were safe, Mr Abbott said he was not going to provide any information ''that gives aid to people smugglers''.

Speaking at the Lowy Institute for International Policy in Sydney, Mr Fraser cited wire reports that a Sri Lankan police chief had said another 41 passengers recently picked up by Australia and returned to Sri Lanka would be prosecuted for leaving the country illegally.

''The other thing [the police chief] said was that they would all be subject to enhanced imprisonment,'' Mr Fraser said. ''What is enhanced imprisonment? Is that a new name for torture? Sounded very like it.''

Lawyers for the government and the 153 asylum seekers on the second boat are still discussing how many of those on board will be able to be interviewed by those who will represent them in a High Court challenge to any attempt to take them to Sri Lanka before their claims are properly processed.

They are expected to reach agreement on Thursday, with a directions hearing expected within three weeks. The interviews will provide the first clues on how the boat was intercepted.