A military defense lawyer said Monday that he has asked the U.S. Supreme Court to halt the upcoming war crimes trial of the youngest detainee at Guantanamo Bay.

The trial is scheduled to begin Aug. 10 for Omar Khadr and it would be the first at the U.S. Navy base under President Barack Obama's administration.

Khadr, son of a slain al-Qaida financier, is accused of throwing a grenade that killed a U.S. soldier in Afghanistan and faces a maximum life sentence if convicted. The Toronto-born inmate was 15 when he was captured in 2002.

His attorney, Army Lt. Col. Jon Jackson, argues that the offshore system for prosecuting terror suspects is unconstitutional. Among other concerns, he said it is unfair because it is reserved only for non-U.S. citizens.

"The military commissions provide young Omar, a Canadian citizen, only second class justice. This kind of discrimination is something we cannot stand for as a country," Jackson said.

Jackson said he filed the emergency petition with the high court Monday because a federal appeals court in Washington had not acted on a request he filed four months ago.