David Cameron pledged to help America "destroy" self-styled Islamic State (IS) extremists in Syria as he gave his clearest signal yet that UK forces could be asked to join air strikes.
The Prime Minister said he wanted Britain to "step up and do more" if he could secure the approval of Parliament as he prepared to issue a stark warning to home-grown would-be jihadists that IS wanted them as "cannon fodder".
He will use a speech tomorrow to set out what aides said would be "significant" elements of the Government's strategy to combat the threat from fundamentalist terrorism for the next five years.
The decision to invite Labour's interim leader Harriet Harman to a National Security Council briefing on the threat last week was seen as a further step to prepare the ground for a possible parliamentary vote to extend air strikes in the autumn.
But ministers will also be forced to explain why RAF pilots were allowed to take part in bombing raids over Syria despite MPs having voted against Britain carrying out strikes in the country.
Downing Street has confirmed that Mr Cameron was aware of the missions flown by a small number of aircrew embedded with US and Canadian forces despite Parliament only authorising attacks on IS targets in neighbouring Iraq.
Asked directly in an interview for US television channel NBC if he planned to join the US-led air raids within Syria, he said: "Look, we know that we have to defeat Isil, we have to destroy this caliphate, whether it is in Iraq or in Syria.
"That is a key part of defeating this terrorist scourge that we face.
"I want Britain to do more. I'll always have to take my parliament with me. We're talking and discussing at the moment, including with the opposition parties in Britain, what more we can do.
"But be it no doubt, we're committed to working with you to destroy the caliphate in both countries," he told the Meet The Press programme to be broadcast today.
In his speech, Mr Cameron will renew his focus on "shared values" and deliver an appeal to all faiths to "support the British way of life".
He will dismiss complaints that new duties on schools to prevent radicalisation amount to spying on Muslim pupils as "paranoia in the extreme" and part of the "ludicrous conspiracy theories" of plots against Islam.
And he will focus his message on convincing those tempted to travel to Syria not to buy into the supposed "glamour" of fighting for IS in the region.
Police and security services believe at least 700 extremists have travelled to fight alongside the self-styled IS and other fundamentalist groups, with around half thought to have returned to the UK.
A growing number of women and girls - 43 in the last year alone - are thought to have gone to the war-torn nation, suggesting families are fleeing there at the rate of one a week.
Most recently police confirmed they were investigating the disappearance of a family of 12 from Luton including four women and three children.
Mr Cameron, who pledged a "full spectrum" response after 30 British tourists were killed by an IS gunman in Tunisia, last month pinned some blame for UK citizens being radicalised on sections of society who "quietly condoned" extremist views.
Every aspect of that ideology has to be taken "to pieces", he will say, according to extracts released in advance.
"The cultish world view, the conspiracy theories, and yes, the so-called glamorous parts of it too," he says.
In a direct appeal to young people tempted to join IS, also known as Isil, he will say: "You won't be some valued member of a movement. You are cannon fodder for them. They will use you.
"If you are a boy, they will brainwash you, strap bombs to your body and blow you up. If you are a girl, they will enslave and abuse you. That is the sick and brutal reality of Isil.
"We must de-glamorise the extremist cause, especially Isil. This isn't a pioneering movement, it is vicious, brutal, fundamentally abhorrent."
Mr Cameron will call on all parts of society to "challenge the ludicrous conspiracy theories of the extremists".
"The world is not conspiring against Islam; the security services aren't behind terrorist attacks; our new Prevent duty for schools is not about criminalising or spying on Muslim children.
"This is paranoia in the extreme.
"In fact that duty will empower parents and teachers to protect children from all forms of extremism – whether Islamist or neo-Nazi."
Local authorities, prisons, NHS trusts and schools have been placed under a statutory duty to prevent extremist radicalisation taking place within their walls.
"We have a very clear creed in our country and we need to promote it much more confidently," he will say.
"Wherever we are from, whatever our background, whatever our religion, there are things we share together.
"We are all British. We respect democracy and the rule of law. We believe in freedom of speech, freedom of worship, equal rights regardless of race, sex, sexuality or faith.
"We believe in respecting different faiths but also expecting those faiths to support the British way of life.
"Whether you are Muslim, Hindu, Jewish, Christian or Sikh, whether you were born here or born abroad, we can all feel part of this country - and we must all now come together and stand up for our values with confidence and pride."