Media playback is unsupported on your device Media caption Tony Blair: "ISIS...kill without mercy and they're prepared to die without regret"

Former Prime Minister Tony Blair has said that sending in combat troops to fight Islamic State militants on the ground should not be ruled out.

Mr Blair said in a BBC interview: "Unless you're prepared to fight these people on the ground, you may contain them but you won't defeat them."

He said there was "no appetite for ground engagement in the West" and that local forces could take on the role.

The jihadists claim to have established a caliphate in Syria and northern Iraq.

Previously known as ISIS, the group has been condemned by the West for its brutal tactics, including on-camera beheadings.

'Fanatical'

While the US and France have launched air strikes against the militants, Mr Blair said bombing alone would "not suffice".

The problem is not that we're facing a fringe of crazy people, a sort of weird cult confined to a few fanatics Tony Blair

The UK government has not ruled out joining air strikes in Iraq or Syria, but has said that targeting IS positions in the latter would be complicated.

Speaking to BBC News, Mr Blair said that it was possible to "harry and hem them [IS militants] in by air power" but at some point "someone's boots on the ground" would be a necessary tactic.

"I'm not saying we in the West need to do this; it would be better if it were done by those people closer to the ground who have got the most immediate and direct interests in fighting them.

"But I don't think we can in all circumstances rule it out and after all we do have the force capability to do this."

Image copyright PA Image caption As prime minister Tony Blair was instrumental in the 2003 US-led invasion of Iraq

Mr Blair's period in office came to be defined by wars in Iraq and Afghanistan.

In a 6,500-word essay published on his Faith Foundation website, he said lessons learned from those conflicts had improved the West's "capacity and capability" to fight IS.

He added that, because groups such as IS were "fanatical", there was no way to defeat them without "a willingness to take casualties in carrying the fight through to the end".

'Root it out'

The UK has supplied arms to Kurdish fighters and has provided logistical support to other groups battling the jihadists in the region.

But repeating his insistence on American news channel CNN that IS could only be confronted with ground troops, Mr Blair added: "I'm sure the leadership of both the US and elsewhere will make sure that whatever is necessary to defeat ISIS is done."

Image copyright Reuters Image caption Islamic State militants made rapid advances in the region over the summer

The IS militant group came to global prominence as it seized large swathes of eastern Syria and northern and western Iraq.

It has become notorious for tactics including mass killings and the persecution of religious minorities.

But in his essay Mr Blair, who has been the UN's Middle East peace envoy since 2007, said: "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."

'Crush them'

He claimed there was a "spectrum of opinion" which "stretches further into parts of Muslim society".

On that spectrum, he said, were those who would oppose extremism, "but who unfortunately share certain elements of the fanatic's world view".

Former director of British special forces in Iraq and Afghanistan, Lieutenant General Sir Graeme Lamb, said the government should say it is prepared to "rule in" forces on the ground to tackle IS.

Speaking to BBC Radio 4's Today programme, he said IS presented themselves as an "unstoppable force" but "we need to crush them".

Sir Graeme said large-scale conventional forces would not be appropriate as IS "do not represent that type of threat". Instead he suggested the UK and US could provide advisers, special forces and airborne brigades.

But he said he had "no difficulty" with including forces for the front line.