The mastermind behind the London bombings, which killed more than 50 people, has been identified, a report said on Thursday.
The British-born man in his 30s arrived at a British port last month and left the country again the day before Thursday's attacks, The Times newspaper reported.
The man is of Pakistani origin, the report said.
The four suspected suicide bombers were also Britons of Pakistani origin.
According to The Times, security sources believe the mastermind was involved in previous terror operations and has links with followers of Osama bin Laden's Al-Qaeda in the United States.
He is thought to have visited the bombers in their home city of Leeds, northern England, and identified targets on the London Underground rail subway system where three of the four bombs exploded, the paper said.
Security sources also said he was likely to have trained the recruits in how to trigger their rucksack-carried bombs, three of which went off almost simultaneously at around 8:50 am, at the peak of last Thursday's morning rush hour.
Police have reportedly switched their investigation towards seeking the mastermind of the bombings since learning that the four bombers killed themselves in the attacks.
Home Secretary Charles Clarke said earlier that the aim was now "to attack the people who are driving, organising and manipulating" bombers.