Omar Khadr is shown in a sketch from a hearing at Guantanamo Bay in January. Ottawa will seek to overturn an appeal court ruling that it must demand his repatriation. (Janet Hamlin/Pool/Associated Press)

The federal government will appeal to the country's top court to quash a ruling forcing Ottawa to press for the release of Canadian Omar Khadr from Guantanamo Bay, the Foreign Affairs Department confirmed Tuesday in a move quickly denounced by opposition parties.

The Federal Court of Appeal this month upheld a lower-court ruling that required Ottawa to try to repatriate Khadr, the only Western citizen still being held by the U.S. at its military base in Cuba.

"After careful consideration of the legal merits of the ruling ... the government has decided to seek leave to appeal the decision to the Supreme Court" of Canada, Foreign Affairs said in a statement.

The government has filed a motion to stay the Appeal Court's decision pending its application to the Supreme Court, the statement said.

Dennis Edney, Khadr's Canadian lawyer, said he will argue that the country's top court should not hear the case.

"We will not make it easy for the government," Edney said from Edmonton. "The ruling indicated this was a unique decision, a one-off decision, based upon the particular circumstances of Canadian conduct and Omar Khadr's situation. It's not an issue of national security, it's not an issue of national importance, and we will be telling the court that."

Public Security Minister Peter Van Loan and Justice Minister Rob Nicholson both deferred questions to Foreign Affairs Minister Lawrence Cannon, who is on a government trip to Turkey and Egypt, and was unavailable to comment.

Opposition parties decried the decision to appeal, saying it goes against the government's legal and moral obligations toward its own citizens.

"We don't minimize the seriousness of the crimes for which Mr. Khadr is originally accused, but he's done … seven, eight years in Guantanamo in horrendous conditions and we think it's time he comes home and be reintegrated," Liberal Leader Michael Ignatieff said.

"It's not just Omar Khadr, it's a question of whether this government stands up for Canadians overseas."

Bloc Québécois House leader Pierre Paquette said the government's move was "totally unacceptable."

"We already have two federal court decisions requiring the government to take all means necessary to repatriate Omar Khadr," Paquette said.

Khadr's family declined to comment on the government's decision.

Toronto-born Khadr, 22, was captured by U.S. soldiers in Afghanistan in 2002, when he was 15, and has been held at Guantanamo Bay for seven years. The U.S. accuses him of throwing a grenade that killed U.S. soldier Christopher Speer, but leaked documents have called into question the Pentagon's murder case against Khadr.

On Aug. 14, the Federal Court of Appeal upheld a Federal Court ruling that ordered Ottawa to press for Khadr's return from Guantanamo.

In a 2-1 judgment, the appeal court found that Khadr's rights under Section 7 of the Charter of Rights and Freedoms — the rights to life, liberty and security of person — had been breached when Canadian officials interviewed him at the prison in Guantanamo in 2003 and shared the resulting information with U.S. authorities.

Other countries have intervened

Some other Western countries have intervened to get their citizens out of Guantanamo, but the Canadian government has maintained that because of the seriousness of the charges, Khadr should face military proceedings in the United States.

"Our position regarding Mr. Khadr remains unchanged," Foreign Affairs said in its statement Tuesday. "Omar Khadr has been accused of serious crimes, including murder."

The federal government is also arguing that the lower courts overstepped their bounds when it comes to Section 7 of the charter, and says that its "duty to protect" citizens doesn't necessarily apply when the citizen is outside the country.

With January's swearing-in of U.S. President Barack Obama, who vowed to close Guantanamo and repatriate all but its most serious prisoners, it seemed the issue of Khadr's detention would soon be immaterial. But the Obama administration has never laid out its intentions for Khadr, and it now seems the Guantanamo tribunals might still proceed.

"President Obama has not communicated any decision to the government of Canada with respect to the case of Mr. Khadr," Foreign Affairs said, adding "it is in our interest to wait for the outcome" of the White House's decisions on the Guantanamo tribunals.

The military commission process, a cornerstone of former president George W. Bush's approach, has been hobbled by court findings that it violates the American constitution, as well as by allegations that it breaches international law and that crucial evidence was extracted under torture — which Khadr's lawyers say happened to him.

Human rights advocates say that because Khadr was 15 when captured, he is entitled to protection under the United Nations Convention on the Rights of the Child, which says anyone under age 18 in armed conflict is to be treated as a victim needing rehabilitation, not as a hostile agent to be imprisoned.

Pentagon changes tune

According to the original U.S. military version of events, Khadr ambushed American soldiers with a grenade following a four-hour firefight against al-Qaeda militants at a mud compound in Afghanistan in 2002.

Pentagon officials later backtracked slightly after it was revealed nobody witnessed Khadr throw the grenade. Military officials said an eyewitness wasn't needed, because Khadr was the only militant left alive and the only person who could have thrown the grenade.

But a classified Pentagon document inadvertently released to reporters in February 2008 suggested otherwise. The document, a sworn first-hand account of the gun battle from an American soldier, said two combatants were left alive in the compound when Speer was killed.