GUANTANAMO BAY, Cuba - A U.S. military official has rejected a clemency appeal from the lone Canadian held at Guantanamo Bay.

The Convening Authority for Military Commissions says Omar Khadr must serve the full eight-year prison term he was sentenced to last October.

Khadr's lawyers had appealed to have the sentence cut in half, arguing improper testimony swayed the jury at his sentencing hearing.

The jury sentenced Khadr to 40 years in prison, but the terms of a pre-trial agreement limited the term to eight years.

Khadr, who was just 15 when he was captured by U.S. forces in 2002, has pleaded guilty to throwing a hand grenade that killed an American soldier.

Khadr has spent the past nine years behind bars at the controversial U.S. naval base and is slated to be transferred to a Canadian prison this year.

One of Khadr's pentagon-appointed lawyers said the rejection of the clemency application marks the final chapter in the complex military commission case.

"While we are disappointed that Omar did not receive clemency, we are confident that the convening authority carefully considered all defence submissions prior to final action," Lt. Col. John Jackson said. "Omar continues to be focused on the future, his education and repatriation to Canada."