Tony Blair has told an emergency session of parliament that there is no doubt that the September 11 attacks were carried out by the al Qaeda organisation headed by the Saudi dissident Osama Bin Laden.

Speaking to MPs, Blair said Bin Laden had worked with the Taliban regime to prepare for the attacks on the US which left up to 7000 people dead.

"It was Bin Laden and al Qaeda, terrorist network which he heads, that planned and carried out the atrocities on September 11. Bin Laden and al Qaeda were able to commit their atrocities because of their close alliance with the Taliban regime in Afghanistan which allows them to operate with impunity in pursuing their terrorist activity."

He said that he was taking the unusual step of placing a detailed report of the evidence against Bin Laden in the House of Commons library. Whilst the report does not make public all the intelligence it does give a clear account of the west's evidence - subject to certain security constraints.

Blair told the Commons of a series of terror attacks masterminded by Bin Laden and said the most recent assaults on the US "bear all the hallmarks of a Bin Laden operation".

Of the 19 hijackers who took place in the attacks, Blair told MPs that three had already been "positively identified" as known associates of bin Laden.

Blair said that in the wake of the "overwhelming" evidence of Bin Laden's involvement that the west's "immediate objectives are clear".

"We must bring Bin Laden and other al Qaeda leaders to justice and eliminate the terrorist threat they pose," he said.

Blair also turned his fire on the Taliban - saying the regime now faced a clear choice.

"We must ensure that Afghanistan ceases to harbour and sustain international terrorism. If the Taliban will not comply with that objective we must bring about a change in that regime to ensure that Afghanistan's links to international terrorism are broken," he told MPs.

He indicated that the first military response to the September 11 attacks on the US could be expected soon.

The Conservative leader, Iain Duncan Smith, said the al Qaeda organisation was "guilty as charged" in respect of the September 11 attacks.

"Our determination to bring the terrorists to justice must not be undiminished," he told MPs.

Duncan Smith said that any military action against al Qaeda or the Taliban would be a "just war".

"This is not about revenge. It is not about retribution. It is not only about justice against one man. It is standing up for what is right against what is wrong. It is about upholding civilised values against anarchy. It is about defending good against the evil of terrorism," he said.

"So today we should reaffirm our single and collective purpose: No excuses should be made, no justification sought and no help offered to those who would carry out such evil deeds - let right be done."

Charles Kennedy, the Lib Dem leader, said the evidence published to the Commons library was "persuasive" but called for more details to be made available as early as possible.

He raised serious humanitarian concerns following reports of a pending refugee catastrophe in Afghanistan.