Mr. Blair spoke as authorities in Britain, Egypt, and Pakistan pursued leads to discover who, besides the suicide bombers, was involved with the July seventh London transit system attacks that killed 55 people.

A London newspaper, The Sunday Times , reported Sunday Britain's domestic intelligence agency, MI5, opened a file last year on one of the suspects, Mohammed Sidique Khan, but closed it after concluding he did not pose a threat.

In Cairo, Egyptian authorities questioned Magdy el-Nashar, a biochemist from Leeds who traveled to Egypt the week before the bombings. British police say they found traces of explosives inside a house rented by Mr. el-Nashar, but Egypt's interior minister dismissed news reports suggesting he built the bombs used in the attacks.

And in Pakistan, officials are investigating contacts made by one of the suspects, Shahzad Tanweer, during two trips to Pakistan in the last two years.