Six Guantanamo Bay detainees have been charged with murder, terrorism and violating the laws of war over the September 11 terror attacks.

US prosecutors will seek the death penalty for what they now term a war crime, but the final decision will rest with judge Susan Crawford, the convening authority for military commissions.

Relatives of British September 11 victims have welcomed news that the six men accused over the attacks could face the death penalty.

US prosecutors have said they will seek the execution of Khalid Sheik Mohammed, the alleged mastermind of the plot, and five other Guantanamo Bay detainees they believe were involved in the 2001 atrocity that killed nearly 3000.

If sent for trial, the six men would be the first detainees to be brought before a military tribunal in Guantanamo Bay in connection with the attacks.

Patricia Bingley, 73, lost her son Kevin Dennis in the tragedy.

The 43-year-old Cantor Fitzgerald employee was on the 101st floor of the north tower of the World Trade Centre when the first plane struck.

She said: "I believe if there is real evidence that these people had any connection, no matter how small, they should be found guilty. I'm not a bit bothered over how they are going to die.

"I always wanted them to go after Bin Laden, that would have been my justice."