The Iraq war was a setback to the ongoing battle against terrorism because it diverted intelligence resources and provided a boost to al-Qaeda's recruitment, a terror expert has told MPs.
Professor Paul Wilkinson of St Andrews University also raised the prospect of a nuclear terror attack in evidence to the Commons Foreign Affairs Select committee.
He said most counter-terrorism experts accepted there was a "significant downside" to the Iraq war and he suggested there still might be terror attacks avenging the conflict.
Prof Wilkinson told the committee: "All of us breathed a great sigh of relief at the fall of the brutal Saddam regime.
Bin Laden may have been boosted by the Iraq war
"[But] most observers on counter-terrorism would accept there was a very significant down-side to the war in Iraq as far as counter-terrorism was concerned."
He added: "It takes time for al-Qaeda to organise major attacks of a specialist nature, often months are involved in terms of preparing the personnel, getting the
weapons in place and so on.
"So we may not have seen the outcome of the plans laid in these recent months of war."
The professor, who heads St Andrew's centre for the study of terrorism and political violence, said al-Qaeda had shown a "great interest" in so-called dirty bombs.
"It is quite possible they have the means to construct a dirty bomb technically," he said.
Prof Wilkinson dismissed suggestions there was a link between Saddam Hussein's regime and al-Qaeda.
Concrete blocks have been placed around Westminster
"The story that there was a collaboration between them was dreamed up in
Washington," he said.
"I don't know who dreamed it up but I have found no substance to it."
Prof Wilkinson also criticised the Afghanistan campaign blaming the escape of Osama Bin Laden on a lack of special forces on the ground when US-led troops were attacking Tora Bora.
Lack of resources?
Warlords in the country had since been able to re-establish their grip on sections of Afghanistan because of a lack of coalition troops in the country.
"There are very limited peacekeeping forces based in the Kabul area," the
He added it would have been "so much better" if more force and more resources had been deployed in Afghanistan.
"It would have been so much better if we had been able to devote some greater
force to the Karzai government to establish control.
The professor said al-Qaeda had 17,000 trained volunteers across 90 countries and it was important not underestimate their strength.
It was the largest international terror organisation the world has seen, he said.