"I can now confirm that of the 19 hijackers identified from the passenger lists of the four planes hijacked in America on the 11th of September, at least three have already been positively identified as known associates of bin Laden with a track record in his camps and organisations," Mr Blair said.
Of those three, one had also been identified as playing a key role in attacks on US embassies in east Africa in 1998 and later on the US warship Cole in Yemen.
Mr Blair also said bin Laden had told associates of a "major operation" before the attacks.
"A range of people were warned to return to Afghanistan because of action on or around September 11. And most importantly, one of bin Laden's closest lieutenants has said clearly that he helped with the planning of the 11 September attacks."
Mr Blair said he would give Parliament a document covering bin Laden's history, and "some of what we know in respect of the 11th of September".
Intelligence and security considerations prevented full disclosure.
Mr Blair spoke before embarking on a mission to stiffen the resolve of potential Muslim allies and ensure a stable platform for military strikes in Afghanistan.
Several Arab and Muslim nations want more evidence than they have seen so far. The Arab world is also concerned that the campaign could broaden to attacks on member countries - particularly Iraq.
US Secretary of Defence Donald Rumsfeld, one of the more hawkish members of the US Administration, is visiting Saudi Arabia, Egypt, Oman and Uzbekistan to confirm the US resolve for military action. Pakistan is conspicuous by its absence from his itinerary, apparently for fear of destabilising the country.
Instead, Mr Blair will fly to Pakistan after meeting Russian President Vladimir Putin in Moscow.
The shuttle diplomacy is to counter what one senior Washington source called "wobbliness in Saudi Arabia and other nations in the region".
Saudi Arabia has refused to allow the US to launch strikes from its bases and Pakistan, which shares strong ties with the Taleban, has placed similar limits on its support for the US.
On a visit to Washington, the Emir of Qatar, Sheikh Hamad bin Khalifa al-Thani, said the Arab and Muslim worlds needed convincing on the international campaign against terrorism.
"What is required now is how we combat terrorism, but in a clear and frank way that convinces everyone, convinces the protesters in America and convinces the Arab world and Islamic world at the same time."
Secretary of State Colin Powell left open the possibility of taking the fight beyond Afghanistan after meeting the Emir, when he said a military strike against al Qaeda would be only the first step.
"We are not looking for conflict with other nations but ... we have to make sure that this campaign focuses on al Qaeda but also takes note of those nations that provide haven ... for terrorist organisations."
- REUTERS
Map: Opposing forces in the war against terror
Afghanistan facts and links
Full coverage: Terror in America