Peace envoy Tony Blair has said The UK and other Western powers should be prepared to commit ground troops to fight against extremists like the Islamic State (IS).
The former prime minister, who earns millions from his consultancy roles and property empire, has said air strikes alone will not be enough to defeat IS or similar groups, and while training and equipping local fighters may work, the option of sending in combat soldiers should not be ruled out.
Blair, whose premiership came to be defined by the Iraq War and who is often blamed for the violent insurgency gripping Iraq after toppling Saddam Hussein in 2003, acknowledged there was "no appetite" for ground engagement against IS but warned: "You cannot uproot this extremism unless you go to where it originates from and fight it."
Blair, The Middle East peace envoy
Blair, who was recently awarded 'Philanthropist of the Year', said the struggle against Islamist extremism should be seen as an international fight rather than a series of isolated conflicts, comparing it to the fascist and communist ideologies of the last century.
In an essay on his Tony Blair Faith Foundation's website the former premier also stressed the importance of engaging with a wider spectrum of radical Islamism, not just the violent fringe.
He said because extremists such as IS - formerly known as Isis - are "fanatical" and "prepared both to kill and to die" there could be no solution that does not involve force "with a willingness to take casualties in carrying the fight through to the end".
"This is where we get to the rub. We have to fight groups like Isis," he said.
Tony Blair after winning the GQ award for best Philanthropist
"There can be an abundance of diplomacy, all necessary relief of humanitarian suffering, every conceivable statement of condemnation which we can muster, but unless they're accompanied by physical combat, we will mitigate the problem but not overcome it."
The US and France have already launched air strikes against IS targets, and the UK has not ruled out joining the bombing campaign against the extremists, who have occupied a large area of Iraq and Syria.
The Government has supplied arms including heavy machine guns to Kurdish fighters on the front line and has also been involved in transporting materiel supplied by other countries.
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But Blair said: "Air power is a major component of this, to be sure, especially with the new weapons available to us. But - and this is the hard truth - air power alone will not suffice. They can be hemmed in, harried and to a degree contained by air power. But they can't be defeated by it.
"If possible, others closer to the field of battle, with a more immediate interest, can be given the weapons and the training to carry the fight; and in some, perhaps many cases, that will work. It may work in the case of Isis.
"There is real evidence that now countries in the Middle East are prepared to shoulder responsibility and I accept fully there is no appetite for ground engagement in the West.
"But we should not rule it out in the future if it is absolutely necessary.
"Provided that there is the consent of the population directly threatened and with the broadest achievable alliance ... we have, on occasions, to play our part."
He said the lessons learned from the wars in Afghanistan and Iraq had improved Western forces' "capacity and capability" to respond to the threat of IS and similar groups.
"To those who say that after the campaigns in Afghanistan and Iraq we have no stomach for such a commitment, I would reply the difficulties we encountered there are in part intrinsic to the nature of the battle being waged," he said.
"And our capacity and capability to wage the battle effectively are second to none in part because of our experience there.
"However we're not talking here about armies of occupation. We are, in certain situations where it is necessary and subject to all proper limitations, talking about committing ground forces, especially those with special capabilities."
In the 6,500-word essay he stressed that the problem went beyond the extremist fringe stretching deep into parts of Muslim society.
"The problem is not that we're facing a fringe of crazy people, a sort of weird cult confined to a few fanatics. If it was, we could probably root it out, kill or imprison its leaders, deter its followers and close the doors to new recruits.
"The problem is that we're facing a spectrum of opinion based on a world view which stretches far further into parts of Muslim society. At the furthest end is the fringe.
"But at the other end are those who may completely oppose some of the things the fringe does and who would never themselves dream of committing acts of violence, but who unfortunately share certain elements of the fanatic's world view."
Those elements included an "innately hostile" view of the West and views about social and political norms "wholly at odds with the way the rest of the world has developed".
He said it was a "fateful error" to attempt to engage with the "spectrum" in the hope of marginalising the extremist fringe.
"All we do is to legitimise the spectrum, which then gives ideological oxygen to the fringe," he said.
"Compile a compendium of all the formal and informal methods of teaching religion in Muslim communities, even in our own countries, and what you will find is much more frightening than you would think: that in many countries, even those considered moderate, there is nonetheless a significant number of young people taught a view of religion and the world that is exclusive, reactionary and - in the context of a world whose hallmark is people mixing together across the boundaries of race and culture - totally contrary to what those young people need to succeed in the 21st century."
But Blair stressed that "Islamism of course is not the same as Islam", which is a "religion of compassion and mercy".
He said: "This is not a clash of civilisations. It is a struggle between those who believe in peaceful co-existence for people of all faiths and none; and extremists who would use religion wrongly as a source of violence and conflict.
"Our enemies are those who would pervert Islam. Our allies are the many Muslims the world over who are the principal victims of such a perversion."
Told that people would think he is the last person they should listen to, given the experiences following the Iraq invasion in 2003, Blair replied on BBC Radio 4's Today programme: "What I say is maybe having been through all of this, having faced these decisions in government and having faced the difficult choices in Iraq after 2003, and when the very type of terrorism that we're facing today we faced then, maybe it's worth appreciating the fact that there are lessons I have learnt from the experience of having gone through the process of taking these decisions, of having to deal with the situation in Iraq where, as I say, precisely the same type of terrorist forces we were facing in Iraq in 2006-07 is exactly what we face now in 2014."