MIAMI (Reuters) - A Saudi Arabian prisoner accused of plotting the deadly attack on the warship USS Cole in 2000 could be executed if he is convicted in the Guantanamo war crimes tribunal, the Pentagon said on Wednesday.

The Pentagon official overseeing the Guantanamo trials formally approved terrorism and murder charges against prisoner Abd al-Rahim al Nashiri, and referred the case for trial by military tribunal as a capital case.

Suicide bombers rammed an explosives-laden boat into the Cole off Yemen, blowing a massive hole in its side and killing 17 U.S. sailors. Nashiri is accused of planning and preparing the attack.

Defense lawyers argued unsuccessfully that he should not face execution because the case was tainted by torture. Nashiri was subjected to waterboarding and mock executions while held at secret CIA prisons after his capture in Dubai in 2002. He was sent to the detention center at the Guantanamo Bay U.S. Naval Base in Cuba in 2006.

Now that the case has been referred for trial, Nashiri is expected to be arraigned at Guantanamo within 30 days.

(Reporting by Jane Sutton; Editing by Cynthia Osterman)