Britain's former prime minister and Middle East peace envoy Tony Blair said Monday that sending ground troops to fight the Islamic State (IS) group should not be ruled out.
Blair, who sent British forces to fight wars in Iraq and Afghanistan, said he knew "as well as anyone" the difficulties of any such move but insisted it should not be discounted.
IS jihadists control large areas of Iraq and Syria and calls for tougher action against them have grown after the beheading of two US journalists and a British aid worker in Syria, captured on graphic videos.
The US has been carrying out air strikes in Iraq since last month against IS, with France joining the aerial attacks from Friday.
"I accept fully there is no appetite for ground engagement in the West," Blair wrote in an essay on the website of the Tony Blair Faith Foundation.
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"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 occasion, to play our part."
He added that air power alone "will not suffice" in the fight against the IS group.
"They can be hemmed in, harried and to a degree contained by air power. But they can't be defeated by it," Blair added.
"You cannot uproot this extremism unless you go to where it originates and fight it."
Blair sees the conflict in Iraq and Syria as part of a wider global problem with radical Islam which also spans unrest in Pakistan, Nigeria, Mali and China's Xinjiang province.
"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," he wrote.