TORONTO - Lawyers for Omar Khadr filed suit Friday in an effort to compel Prime Minister Stephen Harper to demand the Canadian citizen be repatriated from Guantanamo Bay, where he is due to stand trial for "war crimes" before a U.S. military commission in October.

The suit, filed in Federal Court, argues Canada is obliged under international law to ensure Khadr's rehabilitation and social reintegration, given that he was just 15 when he allegedly killed an American medic in Afghanistan in July 2002.

Instead, Canada has left Khadr to languish for almost six years at Guantanamo Bay, where Canadian courts have found he was detained and abused in violation of international law, said his lawyers Dennis Edney and Nate Whitling.

"It is time for Prime Minister Harper to stand up for the rights of a Canadian citizen," the lawyers said in a statement.

Khadr, now 21, is the only western citizen still detained at the infamous prison, which critics and human rights activists have widely condemned as illegal.

Harper, however, has insisted he won't get involved in the case because a legal process against Khadr is underway.

"Canada has sought assurances that Mr. Khadr, under our government, will be treated humanely," Harper said last month, adding Canada had "no real alternative" to the widely condemned American process.

"We are monitoring those legal processes very carefully."

Harper's office said Friday it was sticking with that position but refused to discuss the suit itself.

"This is predictable," Kory Teneycke, Harper's director of communication, told The Canadian Press.

"It's yet another attempt by Mr. Khadr's lawyers to avoid trial."

Teneycke pointed out the charges against Khadr, including murder, are serious.

In an interview, Whitling said he believed the Federal Court had the jurisdiction to force the government to demand Khadr's repatriation and, if necessary, to charge him criminally in Canada.

"We were hoping this would not be necessary," Whitling said. "(But) we think this is a strong claim."

Edney and Whitling noted the Supreme Court of Canada concluded in May that Khadr's detention at Guantanamo Bay violated basic human rights.

More recently, a Federal Court judge found that Khadr's treatment by U.S. authorities -- who deprived him of sleep to soften him up in advance of a 2004 visit by Canadian interrogators -- violated international prohibitions against torture.

Khadr's Pentagon-appointed lawyer, Lt.-Cmdr. Bill Kuebler, said he fully supported the suit filed by the Canadian lawyers.

"Now we know that the Canadian government has known about, facilitated, and helped cover up the torture and abuse of a Canadian citizen," Kuebler said from Washington, D.C.

"This is no longer just a matter of (government) policy."

In June, the Commons foreign affairs committee called on Harper to demand Khadr's release from Guantanamo to face due process under Canadian law.

Khadr's lawyers argue he should have enjoyed special protections as a child soldier since he was 15 when he allegedly committed his crimes.

However, the U.S. has taken the position that he was 16 when he arrived at Guantanamo, and should be treated as an adult.

Although Khadr is alleged to have thrown a hand grenade that killed Sgt. Chris Speer following a four-hour firefight near Khost in Afghanistan, previously secret documents have recently cast doubt on that assertion.

Khadr's case garnered international headlines last month when video of Canada's spy agency interrogating him at Guantanamo Bay in 2003 was shown around the world.

In that video, Khadr is seen at one point crying for his mother.

In Toronto, a judge reserved his decision on whether Khadr's oldest brother, Abdullah Khadr, should be released on bail pending the outcome of his fight to stave off extradition to the United States.

The elder sibling is wanted in the U.S. for allegedly buying weapons for al Qaeda.