The U.S. military filed a murder charge Friday against Omar Khadr, who is the only Canadian imprisoned in the Guantanamo Bay prison and has been there for more than four years.

Khadr, who is now 20 but has been imprisoned since he was 15, is among the first three prisoners to face charges as the military begins a new set of Guantanamo trials after the original ones were halted by the U.S. Supreme Court in 2006.

Nearly 400 men are being held in the U.S. naval prison in Cuba, all accused by the United States of having links to militant groups such as al-Qaeda and the Taliban.

On Friday, chief military prosecutor Morris Davis also filed charges against an Australian prisoner and a prisoner from Yemen.

Khadr, who was born in Toronto and lived for years in various southern Ontario communities, was arrested in Afghanistan in July 2002. The U.S. military alleges that he killed an American medic in a grenade attack, which wounded several other American soldiers.

Khadr has been held ever since in Guantanamo. His lawyers and human rights groups say he has been abused in the prison.

Trials won't start until spring

The charges against Khadr, the Australian and the Yemeni are not considered formal until they are approved by a U.S. Defence Department legal adviser and an official who oversees the trials.

The process should take two weeks, said Davis. He said the trials will not begin until at least the spring.

The chief prosecutor said it made sense to start with charges against Khadr, who is the only Canadian at Guantanamo, and the other two men.

"Those three have been around for a while, and they were prepared and ready to go," he said. Earlier charges against Khadr were dropped

Khadr and nine other prisoners were previously charged with various offenses, but the charges were dropped in June 2006, when the U.S. Supreme Court intervened.

The court ruled that President George W. Bush overstepped his authority when he ordered the initial military tribunals at Guantanamo. The court also said the tribunal rules violated international and U.S. laws.

U.S. Congress passed a new bill authorizing new military hearings, with new rules, and Bush signed it into law in October 2006. Some of the rules have drawn criticisms from activists because they allow for the use of hearsay and coerced evidence.

The military plans to charge 60 to 80 Guantanamo prisoners under the new system.

Khadr has been accused of training with al-Qaeda.

His father, Ahmed Said Khadr, was reportedly a close associate of al-Qaeda leader Osama bin Laden. The elder Khadr, who moved his family from Canada to Afghanistan in the 1980s, was killed in a gun battle in Pakistan in 2003.

One of Omar Khadr's brothers was wounded in the same attack while three others and a sister have been accused of ties to al-Qaeda. The allegations have never been proven in court.

With files from the Associated Press

Commentary: