Prosecutors and defense attorneys have held a session of the Guantanamo war crimes tribunal so shrouded in secrecy that even the defendant wasn't permitted to attend.

There have been closed sessions of the court in the past, but they have been for procedural matters and did not require the exclusion of the defendant. The prosecution said it was necessary to protect national security.

Neither prosecution nor the defense was permitted to disclose the subject of Friday's hearing. Defense attorney Richard Kammen said he couldn't even discuss it with the defendant back in his cell at the U.S. base in Cuba.

The hearing came during pretrial motions in the case of Abd al-Rahim al-Nashiri, who charged with orchestrating the deadly attack on the USS Cole in 2000.