British magistrates have ordered three more men held in custody in connection with the failed July 21 bombings on London's transit system.

The men, first arrested a week ago in the southern coastal city of Brighton, will again appear in court on August 11.

They have been charged under a terrorism law for allegedly withholding information that could help in prosecuting Hamdi Isaac, one of the four accused July 21 bombers.  He is now in custody in Rome.

On Friday, the leaders of a British mosque said they had sent a letter to police two years ago warning them about a group of young Muslim extremists that included one of the suspects in the July 21 bombings.

London police declined to comment on the letter.