Preliminary hearings for the trial of five men charged over the September 11 attacks have been delayed because of tropical storm Isaac.
The alleged mastermind of the attacks, Khalid Sheikh Mohammed, and four co-conspirators are being held at the US-run Guantanamo Bay prison in southeast Cuba.
The prison has been placed on alert due to the approaching storm, which is expected to bring winds of nearly 60mph within 72 hours.
Already postponed due to the Muslim holy month of Ramadan and a technical glitch, the hearings were due to start on Thursday, lasting six days.
But Judge James Pohl issued an order delaying the hearings until further notice "due to weather" and a "concern for the safety and welfare of all personnel".
Tropical Storm Isaac, currently battering the Lesser Antilles in the Caribbean, could become a hurricane and is expected to hit eastern Cuba by early Saturday, according to the Miami-based National Hurricane Centre.
Commanders at Guantanamo have warned military and civilian personnel to prepare emergency shelters and secure loose objects.
About 6,000 people live and work on the US military base. All 168 detainees will be in buildings that can sustain hurricane-force winds, officials said.
There are plans to evacuate about 200 people, including legal teams and relatives of September 11 victims who travelled to the remote base to attend the hearings.
Mohammed is due to stand trial along with his Pakistani nephew Ali Abd al Aziz Ali, also known as Ammar al Baluchi; Mustapha al Hawsawi of Saudi Arabia; and Yemenis Ramzi Binalshibh and Walid bin Attash.
The five face the death penalty if convicted for their roles in the terror attacks by al Qaeda militants in which hijacked planes were used to strike New York, Washington and Shanksville, Pennsylvania, killing 2,976 people.
Their trial is not expected to begin for at least a year.