Boris Johnson has branded religious extremists lured by organisations such as Islamic State (IS) as "w*****s" who are obsessed with pornography.

London's mayor, who is to stand as a Conservative parliamentary candidate in the general election, took aim at Muslim fundamentalists in an interview with The Sun, suggesting they were young men who were low on self-esteem.

Citing an MI5 report into Muslim extremism, according to the paper, Mr Johnson said: "If you look at all the psychological profiling about bombers, they typically will look at porn. They are literally w*****s. Severe onanists. "They are tortured. They will be very badly adjusted in their relations with women, and that is a symptom of their feeling of being failure and that the world is against them. They are not making it with girls and so they turn to other forms of spiritual comfort - which of course is no comfort.

"They are just young men in desperate need of self-esteem who do not have a particular mission in life, who feel that they are losers and this thing makes them feel strong - like winners." He added he felt efforts to tackle extremism should come from within Muslim communities but claimed clerics had not been "persuasive in the right way with these people".

More than 500 Britons are thought to have gone to Syria and Iraq to fight with IS, while a report this week found many Western women in IS were "desensitised" to violence carried out by the militants and encouraged it on social media.

It is not the first time Mr Johnson has been outspoken on terrorism - on a recent visit to the Kurdish regional capital Irbil, he called on the Government to supply sophisticated weaponry to Kurdish peshmerga fighters battling IS terrorists.

But he suggested that ministers were nervous about doing so because they feared they could be used by the Kurds to establish their own separate state, independent of the Iraqi government in Baghdad.

Asked about Mr Johnson's comments, Conservative chairman Grant Shapps said: "We are living in a world where there are brand-new threats in the 21st century ... with these enormous terrorist attacks and what is going on with IS in Syria and Brits going there.

"I think any Brit who leaves and fights against this country's interests like that, I can attach all sorts of words to them. I'm clear that what this country needs to do is absolutely be rigorous about ensuring that people can't just swan back into the country having fought against our national interests.

"Therefore we have things like the counter-terrorist Bill going through Parliament now.

"I think the mood has decisively shifted in favour of people saying 'This country will give all of us our education for free, it will give all of us our health for free, but don't expect to go off and fight against this country's interests and expect to swan back in'. I think Boris's comments will have been driven by that."