A detainee who apparently committed suicide at Guantanamo Bay on Wednesday was a Saudi army veteran who fought for the Taleban, US officials have said.
Mr Amiri was being detained at the new, high-security Camp 5 facility
The man, named as Abd al-Rahman al-Amiri, was found not breathing in his cell at the US detention facility, and guards could not revive him.
Saudi Arabia has said it has begun procedures to repatriate his body.
It was the fourth such death at the camp, where about 380 prisoners are being held without charge or trial.
Two Saudis and a Yemeni prisoner were found hanged in an apparent suicide at Guantanamo in June last year.
A senior US officer caused outrage at the time by describing the suicides of three men as an act of asymmetric warfare and a good PR move on the part of terrorist suspects.
The US authorities would not reveal how the most recent death at the base in Cuba came about, but a spokesman for US Southern Command said Mr Amiri's cell had been "regularly" monitored by guards.
"We will seek to understand what happened and we will seek to prevent it from happening again," Cdr Rick Haupt said.
Cdr Haupt said Mr Amiri was being held in Camp 5, a new, high-security facility within the camp.
Last month, Amnesty International said the new facility "created even harsher and apparently more permanent conditions of extreme isolation and sensory deprivation".
Amnesty said such harsh and inhumane conditions at the camp were "pushing people to the edge".
Cdr Haupt said he did not know if Mr Amiri had attempted suicide before, but the prisoner's records reportedly show he had been on a hunger strike in the past.
He had been force-fed with a nasal tube at the time, Cdr Haupt said.
The US military said Mr Amiri, who served in the Saudi army for nine years, was being held at Guantanamo as an "enemy combatant" for fighting US-led forces north of the Afghan capital, Kabul, and in Tora Bora in 2001.
He also became a mid-level al-Qaeda operative and had met its leader, Osama Bin Laden, it said.
According to records previously released by the US, Mr Amiri acknowledged some of the accusations against him to a personal representative appointed by the military.
He said he went to Afghanistan in 2000 and fought for the Taleban because it was his duty as a Muslim and not because he wanted to attack the US.
"Detainee said had his desire been to fight and kill Americans, he could have done that while he was side by side with them in Saudi Arabia," the transcript said.
"His intent [in travelling to Afghanistan] was to go and fight for a cause that he believed in as a Muslim toward Jihad, not to go and fight against the Americans."
Mr Amiri also told his representative he had attended a "school for jihad" before the invasion and seen Osama Bin Laden "from a distance".
He was captured in Pakistan and transported to Guantanamo in February 2002.