Khalid Sheikh Mohammed
© AFP/Getty Images
Khalid Sheikh Mohammed
U.S. military prosecutors have filed new charges against the self-described mastermind of the September 11 attacks in 2001, Khalid Sheikh Mohammed, and four alleged co-conspirators held at the Guantanamo detention camp.

The conspiracy and mass murder charges were expected to be announced later on Tuesday, according to sources involved in the war crimes tribunals at the U.S. naval base in Guantanamo Bay, Cuba.

During President George W. Bush's administration, all five defendants had been charged in the tribunals with plotting the attacks, which killed nearly 3,000 people in the United States.

The charges, which carried the death penalty, were dropped while President Barack Obama's administration tried to move the trials into the federal civilian court in New York, near the site of the World Trade Center, which was destroyed in the attacks by hijacked aircraft.

Obama yielded to political opposition and announced in April that the prosecutions would be moved back to Guantanamo.

The official overseeing the Guantanamo tribunals, retired Vice Admiral Bruce MacDonald, must sign off on the charges before the case can proceed to trial.

In addition to Mohammed, an al Qaeda leader captured in Pakistan in 2003, the defendants include his nephew, Ali Abdul Aziz Ali, as well as Walid bin Attash, Ramzi Binalshibh and Mustafa Ahmed al Hawsawi.