Miami: An Afghan prisoner died at the Guantanamo detention centre in a recreation yard in an apparent suicide, the US military said on Wednesday.
The prisoner, identified as Inayatullah, a 37-year-old accused of being a member of al Qaeda, was found dead by guards conducting routine checks at the facility.
"An investigation is under way to determine the exact circumstances of what happened," said Navy Commander Tamsen Reese, a spokeswoman at the Guantanamo Bay US Naval Base in Cuba.
The US military`s Southern Command said guards "found the detainee unresponsive and not breathing”, according to a statement. "After extensive lifesaving measures had been exhausted, the detainee was pronounced dead by a physician."
Inayatullah is the eighth prisoner to die at the detention centre since the United States began sending foreign captives with suspected al Qaeda or Taliban links to Guantanamo Bay in January 2002.
Five others died of apparent suicides and two died of natural causes.
Inayatullah was one of the last captives sent to Guantanamo, where the last publicly announced detainee arrival was in March 2008.
The prison camp has held 779 foreign captives since the United States invaded Afghanistan to oust al Qaeda and its Taliban protectors following the September 11, 2001 attacks. It now holds 171.
In March, President Barack Obama lifted a two-year freeze on new military trials at Guantanamo Bay and suggested the US Congress was hurting American national security by blocking his attempts to move some trials into US civilian courts.
Obama had tried and failed to overcome objections by Republicans and some of his fellow Democrats in Congress to transfer some detainees to US prisons.
The Naval Criminal Investigative Service will conduct an investigation after an autopsy by a military pathologist, the military said. Inayatullah`s body will then be prepared for repatriation.
In the statement, the military said Inayatullah admitted to being a planner for al Qaeda`s terrorist operations and helped to coordinate documentation, accommodations and vehicles to smuggle al Qaeda fighters through Afghanistan, Iran, Pakistan and Iraq.
Cuba has repeatedly criticised the Guantanamo base, saying it is an illegal enclave on its territory.