LONDON, July 31 (Xinhuanet) -- A third terror cell is planning multiple suicide bomb attacks against underground trains in central London, the Sunday Times quoted security sources as saying.

    Intelligence about a cell with access to explosives and its plans to unleash a "third wave" of attacks was the trigger of last Thursday's unprecedented security exercise, when 6,000 police, many armed, patrolled across the capital, the report said.

    The newspaper quoted senior police officers as saying there was "specific" intelligence from several sources of an attack planned for that day, contradicting with the police statement that the exercise was simply a precaution.

    A statement by Scotland Yard, headquarters for British Metropolitan Police, has said Thursday's security exercise -- the biggest since World War II -- was simply a precaution aimed at reassuring the public.

    The disclosure came as the anti-terrorist squad of the Metropolitan Police has learnt that Hussain Osman, 27, one of the suspects for the second but failed attacks was detained in Rome, Italy on Friday. Enditem