SAN JUAN, Puerto Rico — The US military filed a murder charge yesterday against the Canadian son of an alleged al-Qaida financier, who was detained as a teen in Afghanistan and has spent almost five years at the US military prison at Guantanamo Bay.Omar Khadr, now 20, allegedly joined the Taliban in Afghanistan and threw a grenade that killed a US Green Beret soldier in July 2002. He was captured as he lay wounded after that firefight, at an al-Qaida compound in eastern Afghanistan.

The US military charged him with murder, attempted murder, providing support to terrorism, conspiracy and spying under rules for military trials adopted last year and first used to try David Hicks, the Australian sentenced to nine months in prison after pleading guilty.

The military said the Toronto-born Khadr would be arraigned within 30 days. He faces a maximum penalty of life imprisonment.

Opponents of the detention centre at Guantanamo Bay criticised authorities for subjecting Khadr to the same military trial system as adult terror suspects. In any other conflict, he would have been treated as a child soldier, said Jumana Musa, advocacy director of Amnesty International.

“This was, in fact, a child,” Musa said. “From the beginning, he was never treated in accordance with his age. He was treated like any adult taken into custody.”

A Pentagon spokesman, Navy Cmdr. Jeffrey Gordon, said Khadr must be held accountable.

“The Defence Department will continue to uphold the law and bring unlawful enemy combatants to justice through the military commissions process,” he said.

The US military said Khadr hurled a grenade that killed Army Sgt. 1st Class Christopher Speer, 28, of Albuquerque, New Mexico, and wounded Army Sgt. Layne Morris, of West Jordan, Utah. The charges say those acts were carried out “in violation of the law of war,” but did not elaborate.

Speer’s widow and Morris filed a civil lawsuit against Khadr and his father. In February, a judge awarded them $102.6 million.

The military alleges that Khadr also conducted surveillance of US troops and planted land mines targeting American convoys.

Khadr allegedly received a month of basic training from al-Qaida in June 2002 that included the use of rocket-propelled grenades, rifles, pistols and explosives, according to the charge sheet signed by Susan J. Crawford, the convening authority for the military commissions.

Several of Khadr’s family members have been accused of ties to Islamic extremists. His Egyptian-born father, Ahmad Said al-Khadr, was killed in Pakistan in 2003 alongside senior al-Qaida operatives. Canada is holding Khadr’s brother Abdullah on a US extradition warrant accusing him of supplying weapons to al-Qaida.