Tony Blair has said he does not regret leading Britain to war in Iraq when he was Prime Minister and has called on the world to take on and defeat Islamic extremists. He believes that, without intervention, the problem will continue to grow in countries such as Afghanistan.

He called for a battle to be waged against militant Islam similar to that fought against revolutionary communism.

In an address last night to a forum on religion and politics in Chicago, Mr Blair said that the world today faced a struggle posed by "an extreme and misguided form of Islam", which threatened the majority of Muslims as well as non-Muslims.

"Our job is simple: it is to support and partner those Muslims who believe deeply in Islam but also who believe in peaceful co-existence, in taking on and defeating the extremists who don't."

The struggle could not be won "without our active and wholehearted participation," he said.

Mr Blair was speaking almost ten years to the day since he gave an address in Chicago at the height of the Kosovo crisis when he set out what he described as a "doctrine of international community" that sought to justify intervention, including military intervention, not only when a nation's interests are directly engaged but also where there exists a humanitarian crisis or gross oppression of a civilian population.

The speech was criticised widely at the time as hopelessly idealistic and even dangerous.

"Probably, in the light of events since then, some would feel vindicated," Mr Blair said last night, but he stood by his stance. 'I still believe that those who oppress and brutalise their citizens are better put out of power than kept in it,' he said.

Defending his intervention in Iraq and Afghanistan, he said the argument that Britain should revert to a more traditional, cautious foreign policy should be resisted.

"The case for the doctrine I advocated ten years ago remains as strong now as it was then," he said, arguing that there was a link between the murders in Mumbai, the terror attacks in Iraq and Afghanistan, the attempts to destabilise countries such as Yemen, and the training camps of insurgents in Somalia.

"It is not one movement. There is no defined command and control. But there is a shared ideology. There are many links criss-crossing the map of Jihadist extremism. And there are elements in the leadership of a major country, namely Iran, that can support and succour its practitioners."

Defending the Obama Administration's attempts to engage with Iran, Mr Blair said: "The Iranian Government should not be able to claim that we have refused the opportunity for constructive dialogue, and the stature and importance of such an ancient and extraordinary civilisation means that as a nation, Iran should command respect and be accorded its proper place in the world's affairs." I hope this engagement succeeds.