Former British prime minister Tony Blair has urged a deal with Bashar al-Assad in Syria and further NATO involvement in Libya as part of a "titanic" struggle against radical Islam.

Mr Blair said the West had to focus its efforts on tackling religious extremism, insisting it lay behind most of world's most intractable problems.

Failure to shake off the legacy of Iraq and "take sides" with moderates in the Middle East and beyond could mean the 21st Century is dominated by conflict rather than peaceful co-operation, he warned in a speech to Bloomberg in London.

Mr Blair described a global crisis with its roots in "a radicalised and politicised view of Islam, an ideology that distorts and warps Islam's true message".

"The threat of this radical Islam is not abating. It is growing. It is spreading across the world," he said.

"It is destabilising communities and even nations. It is undermining the possibility of peaceful co-existence in an era of globalisation.

"And in the face of this threat we seem curiously reluctant to acknowledge it and powerless to counter it effectively."

Mr Blair, who is Middle East envoy for the quartet of the United Nations, EU, US and Russia, stressed the need for the issue to be at the "top of the agenda".

He insisted that tension with Russian President Vladimir Putin should not be allowed to prevent co-operation to address the problem.

Conceding that recent conflicts such as Iraq had eroded the willingness of Western nations to act, Mr Blair said he hoped those interventions would be seen differently in future.

"There is no commitment that doesn't mean taking a risk," he said.

"It does not mean that we have to repeat the enormous commitment of Iraq and Afghanistan. It may well be that in time people come to view the impact of those engagements differently.

"But there is no need, let alone appetite, to do that.

"I completely understand why our people feel they have done enough, more than enough.

"And when they read of those we have tried to help spurning our help, criticising us, even trying to kill us, they're entitled to feel aggrieved and to say 'We're out'.

"However, as the Afghans who braved everything to vote show us, and the Iraqis who will also come out and vote despite all the threats and the inadequacy of the system they now live in demonstrate, those who spurn our help are only part of the story.

"There are others whose spirit and determination stay undaunted.

"This is not a mess where everyone is as bad as each other. In other words, it matters and there is a side we should be proud to take."

Choice between authoritarian system and hard-liners

Mr Blair said a "perverse" interpretation of Islam had often left people in the Middle East facing a choice between a relatively tolerant authoritarian system and a hard-line theocracy.

Setting out his views on a range of troubled countries, Mr Blair insisted that the West had to be consistent in supporting the principles of religious freedom and rule-based democracies.

In relation to Libya, he said that meant recognising we bore a "responsibility" for the chaotic situation that has developed since Colonel Muammar Gaddafi was overthrown.

"Their urgent need is for security sector reform. We have made some attempts to do so," he said.

"But obviously the scale of the task and the complications of the militia make it very hard.

"But Libya is not Iraq or Afghanistan. It is not impossible to help and NATO has the capability to do so.

"However reluctant we are to make this commitment, we have to recognise the de-stabilising impact Libya is having at present.

"If it disintegrates completely, it will affect the whole of the region around it and feed the instability in sub-Saharan Africa."

Mr Blair branded the turmoil in Syria "an unmitigated disaster", calling for a settlement with President Assad, whom he has previously condemned.

"We are now in a position where both Assad staying and the opposition taking over seem bad options," he said.

"The former is responsible for creating this situation. But the truth is that there are so many fissures and problems around elements within the opposition that people are rightly wary now of any solution that is an outright victory for either side.

 "Repugnant though it may seem, the only way forward is to conclude the best agreement possible even if it means in the interim President Assad stays for a period.

"Should even this not be acceptable to him, we should consider active measures to help the opposition and force him to the negotiating table, including no-fly zones whilst making it clear that the extremist groups should receive no support from any of the surrounding nations."