SAN JUAN, Puerto Rico — The American military is investigating how guards failed to prevent the death last month of a Guantanamo Bay detainee, an apparent suicide in one of the most closely monitored detention camps for suspected Al Qaeda and Taliban members, the top commander said yesterday.

Abdul Rahman Maadha al-Amry, a Saudi who had insisted he was only a Taliban foot soldier, died at the military base in southeastern Cuba on May 30. The military has refused to describe how he died, other than that to say it was an apparent suicide.

In an interview with the Associated Press, Navy Rear Admiral Mark Buzby, commander of Joint Task Force-Guantanamo, said Amry “used items that he had at his disposal there in the cell” to kill himself. He declined to elaborate, citing pending investigations.

“There are actually two investigations going on right now to determine exactly what the circumstances were for both the guard participation and what the detainee did,” Admiral Buzby said by telephone from Guantanamo Bay.

Admiral Buzby said the detainee had been locked up in Camp 5, where high-value and noncompliant detainees are monitored every few minutes by guards.

After three detainees hanged themselves last year — the first suicides since the Guantanamo Bay detention camp opened five years ago — commanders took steps to prevent more suicides, including removing bed sheets when detainees are not sleeping.

Yet somehow, guards who rotate past the cell doors at Camp 5 and peer in at detainees didn’t get to Amry in time to stop him, Admiral Buzby said, adding that the military needs “to understand how he did what he did within the revisit time.”