An armed policeman stands guard outside the Belmarsh Magistrates court in London

Three men charged with attempted murder in last month's bungled bombings on London's transport system have appeared in a high security court.

The suspects were transported under heavy police guard to the high security Belmarsh prison in east London for their arraignment hearings.

A judge ordered all three men to be held without bail until their next court date, on November 14.

The accused are Muktar Said Ibrahim, 27, Ramzi Mohammed, 23, and Yassin Hassan Omar, 24 

They are charged with attempted murder, conspiracy to murder, and possession of explosives stemming from a failed effort to blow up subway trains and a bus on the London transit system on July 21.

A fourth suspect, Hamdi Issac, 27, is jailed in Italy pending a British extradition request.

Police say the July 21 incidents were an attempt to repeat the bombings of July 7, when four British Muslim suicide bombers killed 52 mass transit passengers in London's deadliest ever terrorist attack.

Police and security experts warn Britain could face even more terrorist action.

"These attacks may have been planned for several years. So it's a case of international terrorism can have waves of attacks, but we have to look very carefully at targets," said Sally Leivesley, a London-based risk analyst. "It may not be the same target. It may not be the same type of people. So, that means the public has to be very flexible in where it's looking out for a problem. City buildings. You can have vehicle bombs, for example. So you need to know where to go and what to do."

In other court action, a suspected British Muslim militant appeared before a London judge following a request from the United States that the man be extradited.

The suspect, Haroon Rashid Aswat, is accused of trying to set up a terrorist training camp in the northwestern U.S. state of Oregon, a charge he denies.

He was returned to Britain on Sunday after Zambia deported him. He has been remanded into custody until another court hearing on Thursday.

There have been newspaper reports that Haroon Rashid Aswat was the mastermind behind the deadly July 7 bombings, but London police have played down the reports, calling them "media speculation."