The U.S. military says a Saudi Arabian detainee died of an apparent suicide in his cell at Guantanamo Bay early Wednesday, FOX News confirms.

The detainee was found unresponsive and not breathing in his cell by guards, according to U.S. Southern Command, which oversees the military prison on the U.S. Naval Base in southeast Cuba. Attempts to revive him were not successful.

"They tried to save his life but he was pronounced dead," said Mario Alvarez, a Miami-based spokesman for the command.

The Naval Criminal Investigative Service has initiated an investigation of the incident to determine the circumstances surrounding the death, FOX News confirms. The Service is also conducting an ongoing investigation into the three previous suicides.

According to FOX News sources, he was not a "high value detainee" or "big fish," but an Al Qaeda foot soldier among those picked up fleeing towards Pakistan from Afghanistan after the U.S. invasion.

It was the fourth suicide at Guantanamo since the prison camp opened in January 2002. On June 10, 2006, two Saudi detainees and one Yemeni hanged themselves with sheets. Details, including the prisoner's name and manner of death, were not released.

The death came as the U.S. military prepared to try two detainees — Salim Ahmed Hamdan, a Yemeni, and Omar Khadr, a Canadian who was 15 when he was captured in a firefight with U.S. troops in Afghanistan. Their arraignment is scheduled to proceed on Monday at Guantanamo as planned, Navy Cmdr. Jeffrey Gordon, a Pentagon spokesman, said late Wednesday.

Khadr on Wednesday fired his American attorneys, leaving him without defense counsel as his arraignment approaches, his former U.S. military attorney said.

"He doesn't trust American lawyers, and I don't particularly blame him," said U.S. Marine Lt. Col. Colby Vokey, who was taken off the case Wednesday. "The United States is responsible for his interrogation and his treatment under a process that is patently unfair."

The military toughened security at the prison camp following the previous suicides and an uprising last spring, taking measures to remove access to light fixtures and other possible makeshift weapons.

About 380 men are held at the isolated prison camp on suspicion of links to Al Qaeda or the Taliban.

A cultural adviser was helping the military handle the remains. "The remains of the deceased detainee are being treated with the utmost respect," the military said.

The Associated Press contributed to this report.