Boris Johnson has described men who join religious extremist groups such as Islamic State as "losers" who are likely to be users of pornography.
The Mayor of London told The Sun those turning to violence had low self-esteem and were unsuccessful with women.
The Tory politician cited an MI5 report into extremism that had compiled psychological profiles of jihadists.
Chancellor George Osborne said the mayor was "right not to be nice about these people".
According to the newspaper, Mr Johnson said: "If you look at all the psychological profiling about bombers, they typically will look at porn.
"They are tortured. They will be very badly adjusted in their relations with women, and that is a symptom of their feeling of being failures 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."
Mr Johnson said he believed Muslim communities should lead efforts to tackle extremism, but claimed clerics had not been "persuasive in the right way with these people".
Mr Osborne, speaking on a visit to Portsmouth, said the mayor was known for his "colourful language" but agreed with the sentiment of the remarks.
