The Gillard government is grappling with a United Nations inquiry into its alleged failure to protect David Hicks's human rights. But it has indicated to his supporters that it accepts the United States' denial of his torture and warned the proceeds of his book may be confiscated.

A confidential, 107-page document submitted to the UN on Hicks's behalf by the Sydney barrister Ben Saul details alleged breaches of international law by the US and Australian governments, including a failure to protect his right to a fair trial and freedom from torture.

Hicks says he was brutally bashed, sustained fractured bones and was subjected to sexual abuse and other torture while held captive in Guantanamo Bay as a terrorism suspect.

But the Prime Minister, Julia Gillard, has taken a hard line on Hicks while responding to a letter from a human rights group, the Justice Campaign, whose signatories include the former judges John Dowd and Elizabeth Evatt and a former Guantanamo Bay guard, Brandon Neely. Their letter asks for an open investigation into Hicks's alleged torture and ''illegal'' conviction and calls for an end to any proceeds-of-crime action against his book, Guantanamo: My Journey.

In her response to one of the signatories, the NSW MP and Sydney lord mayor Clover Moore, the Prime Minister says two US investigations have found no evidence of torture, adding: ''At this stage, I do not intend to establish an inquiry into Mr Hicks' detention.''

Hicks was convicted of providing material support for terrorism but his legal team said he only accepted this under a plea bargain because he was desperate to be released from Guantanamo Bay in 2007.

Gillard tells Moore that while Hicks is entitled to publish his book, any profits may be confiscated. Such action would be at the discretion of the Commonwealth Director of Public Prosecutions. Gillard adds that she cannot comment on Hicks's conviction because it was under US law.

Her senior ministers Robert McClelland and Kevin Rudd, while in opposition in 2003, were strident in their criticism of the Howard government's treatment of Hicks, pointing to the illegitimacy of the military commissions which allowed evidence obtained under torture and hearsay evidence.

Now McClelland is Attorney-General. In response to questions about the legitimacy of the conviction and the torture claims, his office reiterated the findings of the two US torture investigations.

But a spokesman revealed: ''Mr Hicks has submitted a communication to the UN Human Rights Committee, which the government will respond to.'' He added: ''That's all we have to say at this stage.''

Saul, working for Hicks in conjunction with Gilbert & Tobin, said there was ''a contradiction in the government's response compared to when they were in opposition''. He said he was not surprised ''they cut a deal'' with Mamdouh Habib - the cleared terrorism suspect who alleges he was abused while held captive in Egypt - to avoid ''inevitable political embarrassment given Habib had launched proceedings in the Federal Court''.

Launching court action is not an option for Hicks. He waived this right as part of the plea bargain.

The military commission under which Hicks's conviction was secured was disbanded by the US President, Barack Obama, who said it did not establish a legitimate legal framework. Hicks's US military defence lawyer, Major Michael Mori, had said there was no doubt his client was assaulted and mistreated.

Saul says the offence of which Hicks was convicted did not exist in law at the time.

Key hearsay evidence against Hicks was subsequently repudiated by the British Guantanamo detainee Feroz Abbasi. He said he regretted his fabrications about Hicks but had co-operated with interrogators because he was being abused and drugged and they had convinced him that Hicks was providing evidence against him.

Asked why this evidence was not referred to in the UN complaint, Saul said: ''None of this was included in the charge sheet as there was no trial, no indication of the provenance of the evidence and no testing of the evidence.''

The government had six months to respond to the UN but it has sought a three-month extension to mid-August.

The leading silk Brett Walker, SC, meanwhile, is understood to be lining up to take on the government should the proceeds-of-crime action be launched. Legal opinions other than Saul's have indicated that proceeds-of-crime action against Hicks's book would struggle because of the difficulty in establishing ''the soundness and validity'' of his conviction in Guantanamo Bay. They also argue it may be hard to deny public interest in Hicks's story, which prosecutors must consider when launching proceeds-of-crime cases.

PM's hard line on Hicks