A taped confession by the self-proclaimed mastermind of the Sept. 11, 2001 terrorist attacks has sparked an internal debate at the Pentagon, with some officials fearing that its release could boost morale for his supporters, a military spokesman said Tuesday.

For now, the U.S. has decided not to release the audiotape of Khalid Sheikh Mohammed from a March hearing at Guantanamo Bay in which he claims involvement in 31 terrorist plots, Pentagon spokesman Bryan Whitman told reporters in Washington.

"You can imagine there certainly are concerns about how an audio recording of that nature might be used by adversaries to embolden their efforts," Whitman said.

The so-called Combatant Status Review Tribunals for 14 "high value" detainees who were taken to Guantanamo last year have been held in secret. Reporters have been barred from attending them, but had been allowed to cover previous hearings for other Guantanamo detainees.

The U.S. has already released a transcript of the hearing, but his allegations that he was tortured in CIA custody were censored by the military. The hearing was held to determine whether Mohammed is an enemy combatant who should continue to be held at the detention center at the U.S. Navy base in Guantanamo Bay, Cuba.

"It's one thing to have a written transcript; it's another one to have somebody's own voice," Whitman said.

The taped hearing of another so-called "high-value" detainee, alleged senior Al Qaeda leader Abu Faraj al-Libi, was released by the Pentagon earlier this month.

Mohammed and al-Libi were among 14 so-called high-value detainees transferred to the U.S. military prison at Guantanamo Bay last September after being held by the CIA in secret locations abroad.

About 380 men are held at Guantanamo Bay, most accused of links to Al Qaeda or the Taliban. Many have been held at the prison for more than five years.

Only three have been charged with crimes.

An appeals court in Kuwait City on Tuesday upheld the acquittal of two former Guantanamo prisoners held for allegedly joining Al Qaeda or the Taliban in Afghanistan.

The two former detainees, Omar Rajab Amin, 41, and Abdullah Kamel al-Kundari, 32, had denied any terror connections, and their lawyers argued the prosecution failed to provide any evidence against the men who they said went to Afghanistan for charity work, not to fight.

The brief ruling, announced by a court clerk, did not give any details. Kuwaiti courts rarely publicize the details of a case on the same day as the ruling.