|A British Metropolitan Police handout photo issued 16 July 2005 shows a CCTV image of the four suspected London suicide bombers, arriving at Luton train station at 07:21 on July 07.|
The report, by an influential parliamentary committee, pointed out that investigations were underway to establish the precise degree of any Al-Qaeda involvement in Britain's worst terrorist attack, which killed 56 people.
In the first full official account of the events leading up to July 7 and its aftermath, the report said Mohammad Sidique Khan, 30, and Shehzad Tanweer, 22 -- two of the four bombers -- were known to have been in Pakistan from November 2004 and February 2005.
"It has not yet been established who they met in Pakistan, but it is assessed as likely that they had some contact with Al-Qaeda figures, the 44-page report by the Intelligence and Security Committee said.
The two men probably received "operational training" there, it said.
At the same time, the committee dismissed theories which circulated after the bombings of a fifth bomber or "mastermind" who may have subsequently fled the country.
The report revealed that Khan and Tanweer had come to the attention of British intelligence prior to the attack.
"At that time their identities were unknown to the security service and there was no appreciation of their subsequent significance," it said, adding nothing was done about them because "there were more pressing priorities."
"Nonetheless, we conclude that, in the light of the other priority investigations being conducted and the limitations on security service resources, the decisions not to give greater investigative priority to these two individuals were understandable."
Khan and Tanweer, along with Hasib Hussain, 18, and Germaine Lindsay, 19, blew up three London Underground trains and a double-decker bus during the morning rush hour on July 7, 2005 by detonating bombs packed into rucksacks.
The report identified a lack of resources available to the intelligence agencies, namely Britain's domestic spy service MI5, to tackle the threat of terrorism.
"The story of what was known about the 7 July group prior to July indicates that if more resources had been in place sooner the chances of preventing the July attacks could have increased," the text said.
"Greater coverage in Pakistan, or more resources generally in the UK, might have alerted the agencies to the intentional of the July 7 group."
The committee's report will be followed by an official government narrative of the attack, due for release at 1230 GMT Thursday.
The two reports were launched last year after the government ruled out a public inquiry into the attacks, despite calls from families of the 52 people who perished apart from the bombers as well as the 700 who were injured for such an investigation.