Parents will be given new rights to have their own children's passports removed to stop them running away to join Islamic State, David Cameron has said.
The move forms part of a new counter-extremism strategy which will also include measures to target "influencers" who seek to radicalise young people while stopping short of advocating violence, said the Prime Minister.
In a high-profile speech in Birmingham, Mr Cameron said Britain was engaged in "the struggle of our generation" against Islamist extremism.
The new strategy, to be published in detail in the autumn, would set out steps to "de-glamourise" IS - also known as Isil, Isis or Daesh - "enforce" British values and put key non-violent extremists "out of action".
Mr Cameron said some of those worst affected by extremism were Muslim parents "living in fear that their children could be radicalised", with up to 700 Britons already believed to have travelled abroad to join IS.
The strategy will include measures to break down segregation in social housing and state schools, as well as a new review on boosting opportunity and integration for minority groups, he said.
But Muslim Council of Britain (MCB) secretary general Shuja Shafi voiced worry that the PM was setting "new litmus tests which may brand us all as extremists, even though we uphold and celebrate the rule of law, democracy and rights for all".
While the MCB agreed IS was "abhorrent", it was vital to "define tightly and closely what extremism is rather than perpetuate a deep misunderstanding of Islam", he said.
Mr Cameron said opposition to IS was not enough to prove a group or individual was non-extremist. They should also reject anti-semitism and sectarianism and condemn conspiracy theories which accuse the West or Jews of seeking to destroy Islam or claim Muslim beliefs are incompatible with liberal societies.
"We need to put out of action the key extremist influencers who are careful to operate just inside the law but who clearly detest British society and everything we stand for," said the Prime Minister.
"These people aren't just extremists, they are also despicable far-right groups too, and what links them all is their aim to groom young people and brainwash their minds."
He rejected arguments that support for violent extremism was driven by grievance over Western foreign policy and the Iraq War.
Instead, he insisted that "the root cause of the threat we face is the extremist ideology itself", which he acknowledged could seem "energising" to young people who had been led towards radicalism.
A new Extremism Bill will include "narrowly-targeted" powers to tackle "facilitators and cult leaders" and stop them "peddling their hatred", said Mr Cameron.
He called on universities to challenge extremist speakers on campus and internet companies to go "much further" in protecting users from exposure to extremist material. And he accused the National Union of Students of bringing "shame" on itself by "allying" with Muslim advocacy organisation Cage, one of whose officials earlier this year described the IS terrorist nicknamed Jihadi John as a "beautiful young man".
Broadcasters should use a wider range of speakers from Muslim communities, rather than repeatedly putting extreme voices on screen, while the Government would give communications watchdog Ofcom stronger powers to deal with militant messages on foreign TV channels broadcasting to the UK online.
And there would be a "total rethink" of efforts in prison to combat radicalisation.
Mr Cameron said that too often the authorities had "turned a blind eye" to issues like forced marriage or female genital mutilation (FGM) for fear of offending cultural sensitivities.
Announcing a consultation on lifetime anonymity for victims of forced marriage, he said he wanted to see more prosecutions as part of a drive to "enforce" British values.
"My argument with young people being sucked towards this appalling extremist Isil worldview is 'You are heading towards a belief system that believes in throwing people off buildings, raping children, enslaving women'," said the Prime Minister.
"The values of freedom and democracy are far stronger, far better than the values of Isil.
"Our values are so great that we should want to enforce them for all, including new arrivals, including people subjected potentially to those practices."