Not enough is being done to prevent people leaving the UK to join Islamic State in Iraq and Syria, a group of MPs has warned.
Keith Vaz, chairman of the Home Affairs Select Committee, said Britain must win their "hearts and minds".
The committee's report comes as the BBC launches a database tracking British jihadists in Syria and Iraq.
It shows that many people left in clusters from certain UK areas - often due to friendships and peer groups.
The MPs' report argues that preventative work with communities, families and international partners is "vital" and needs to be a top priority for the Home Office.
"The number of cases being brought to public attention should ring alarm bells," said Labour MP Mr Vaz.
"This must be a relentless battle for hearts and minds, and without a strong counter-narrative we are in danger of failing to prevent even more departures. We are at the edge of a cliff."
The BBC has been tracking the stories of the men, women, boys and girls who have gone to Syria and Iraq to understand why they go, where they go from and what happens to them.
By analysing around 160 profiles, it reveals the way in which people have travelled in clusters - a group of three young friends from Coventry, another group from Portsmouth, drawn out by one person they knew, others in Cardiff linked to people involved in an extremist organisation.
Social media might play a part but face-to-face contact appears just as, if not more, important, according to the database.
Tracking Britain's jihadists
It includes the stories of:
- 36 who are reported to have died
- 13 who have been convicted by the courts in England
- Many others the BBC has established to be alive and active in Syria or Iraq
The BBC research emphasises the extent to which real-world contacts, rather than just online connections, are often a key driver of radicalisation and intent to travel to Iraq and Syria.
Some of the experts who appeared before the Home Affairs Committee also argued the internet was a secondary influence.
They said that universities and prisons were among the two most significant places where radicalisation occurred.
A spokesman for the Metropolitan Police, which was not aware of the MPs' report, said it would have "welcomed the opportunity" to have given evidence to the committee and that it planned to look at the report in detail.
The disappearance of schoolgirls Shamima Begum, Amira Abase, both 15, and Kadiza Sultana, 16, from east London in February, raised questions as to who could have done more to prevent their departure.
After taking evidence from the police and the families of the girls among others, Mr Vaz said their case suffered from a "lack of immediate action".
He added: "Schools and the police must inform parents immediately, and work with them even if there is the smallest hint of radicalisation, or a close association with someone who is thought to have been radicalised."
However, the Met Police spokesman defended the speed of the police response to the schoolgirls' disappearance. He said the committee's criticism was "misleading", pointing to the evidence given by both UK and Turkish authorities of "rapid exchanges" between the two.
The committee's report said there needed to be an advice service which would be a less extreme step than calling the anti-terrorist hotline.
The Association of Chief Police Officers lead officer for the government's anti-terror strategy Prevent, Chief Constable Sir Peter Fahy, agreed that more needed to be done.
However, he said the police "do not have the capacity" to routinely work with every school in the country.
He added: "The police service will play its part but the prime responsibility for dissuading young people from getting involved in extremist activity has to lie with parents, families and carers."
Sources for BBC database:
- Information provided in open court, or by governments or security agencies
- Information volunteered by relatives
- BBC research to verify individual accounts
- Information from other credible sources who have assisted the BBC
The committee also pointed to weaknesses in information sharing with airlines and other countries.
It said greater care needed to be taken at airport check-in desks when people were travelling to destinations of concern - namely Syria, Somalia, Iraq and Nigeria, as well as neighbouring countries, such as Turkey.
The report said police also needed to work faster to alert overseas partners and airlines when there were concerns over individuals.
There were signs that some of the girls had followed extremist accounts on social media, the report said.
The committee said that social media companies, such as Facebook and Twitter, should be prepared to suspend accounts when there is evidence they are being used to promote violent extremism.
The report also said it was disappointed the Home Office had not implemented a programme for individuals returning to Britain where there is evidence they had fought in Syria.
'Strongest possible action'
Security officials estimate that some 600 Britons have left the country to join IS - and while around half may have returned, many are still out there - and some have died.
The BBC project includes detailed profiles of individuals which can be searched, based on hometown, age and gender, as well as those who have been convicted in the courts or who are believed to have been killed.
A Home Office spokesperson said: "Our priority is to dissuade people from travelling to these areas of conflict, and the Prevent strategy is working to identify and support individuals at risk of radicalisation. The new legal duties we have introduced on public bodies will help strengthen this work.
"The recent Counter-Terrorism and Security Act has also added measures to disrupt travel, including a new temporary passport seizure power. We continue to work with the airline industry to develop new arrangements to ensure that young people at risk are properly identified.
"It's vital that if families are worried that a loved one may be at risk they should contact the police."