Prime Minister David Cameron will on Friday call on Muslim communities and families to do more to help tackle extremism, warning that some risk encouraging young people to be radicalized by giving weight to such views.

Cameron will highlight two cases this week - a 17-year-old from Northern England who blew himself up in Iraq and three sisters who abandoned their husbands and are believed to be bound for Syria with their nine children - as examples of how people can slide from prejudice to extremism.

He will tell a security conference that people who, by way of example, believe democracy is wrong, women are inferior and religious doctrine trumps the rule of law, share the ideology of Islamist extremists.

"There are people who hold some of these views who don't go as far as advocating violence, but do buy into some of these prejudices giving the extreme Islamist narrative weight and telling fellow Muslims 'you are part of this'," he will say in a speech to the GLOBSEC conference in Bratislava, Slovakia.

"This paves the way for young people to turn simmering prejudice into murderous intent ... Part of the reason it's so potent is that it has been given this credence," he will add, according to extracts released in advance by his office.

Cameron will warn that a troubled boy or girl will find it less of a leap to go from British teenager to Islamic State fighter or wife if such beliefs are "quietly condoned online or perhaps even in parts of your local community".

While the government has a role to play in tackling radicalization, so too do communities and families, he will say.

"We need to have a frank debate about the role that everyone has to play," a source in Cameron's office said.

"Part of this is encouraging people in those communities who want to help tackle this radicalization of young people to come forward and help work together on this."