An unprecedented police appeal calling on Muslim women to urge their relatives not to fight in Syria has been criticised as not helpful by a relative of a Briton killed in the war.
Counter terrorism officers have launched the national campaign in the wake of a string of deaths of British men killed on the war-torn country's battlefield.
They warn that young, idealistic men are being radicalised on social networking sites and sucked into the bloody fight against President Bashar Assad's regime.
The national campaign, launched at a series of police-backed events today, is calling on women to do more to stop British Muslims joining the Syrian ranks.
But critics said families would be reluctant to report their relatives to the police in case they became the target of criminal investigations.
Amina Deghayes, whose 18 year-old nephew Abdullah Deghayes was killed in a gunfight in Syria earlier this month, said today's announcement failed to provide a concrete solution to the problem of young men flocking to fight in the civil war.
And she warned that families are already urging their loved ones not to fight, but too often their appeals fall on deaf ears.
She said: "If the steps are to speak to the guys before they leave, I think people already have - they do not need the Government to tell them that.
"In the case of my nephew, he ran away. At what point would we speak to him? I am not being negative. Maybe the actual details of the proposals are more useful than that, but at the moment I haven't heard anything helpful or useful - it would be better than criminalising them, which is the only thing that is going on."
Abdullah's two brothers, Jaffar, 16, and 20-year-old Amer, have also travelled to Syria to fight. Despite desperate pleas from their family, they have refused to return home from the frontline.
Ms Deghayes said: "Everyone in the family has spoken to my nephews, their mum has been speaking to them, their father has tried to bring them back. What can we do if they think they know better, they think they understand it and it's going to make a difference?
"The problem is they are playing with fire, it's very complicated stuff."
Police have warned that Britons caught fighting in Syria are crossing a "red line" and will be investigated.
But Ms Deghayes warned such tough talk could backfire and lead to UK fighters staying in the country to avoid arrest.
She said: "Even if one of them was to consider coming back, they will have to think 'Am I going to prison?'. Fair enough, that may be a consequence of their actions but we have to think of the implications."
Home Affairs Select Committee chairman Keith Vaz said it was unlikely parents would report suspicions about their children to the authorities.
He said: "All the evidence indicates that the families themselves are the last to know,.
"They are also most unlikely to tell the police. The police are not the Samaritans, they are the first step in the criminal enforcement process."
But Helen Ball, senior national coordinator for counter terrorism, said the initiative could be crucial in dissuading vulnerable Britons from being sucked into the bloody war.
And she warned that current estimates that a few hundred Britons have travelled to Syria could be an underestimate and the actual figure far higher.
She said: "Both the material out there on social media and some of the media coverage talking to people out there, it seems to me to show people, whether they were radicalised before they went to Syria, it does show radical people.
"I'm very concerned about that.
"People travelling out to Syria are going to a community where they are complete strangers.
"It is likely they are going to be preyed upon by terrorist groups operating there. If so, they might be brutalised. It is about preventing tragedies."
The counter terrorism chief said she was "very concerned indeed" at the growing numbers of British recruits joining the Syrian ranks.
Police said 40 people had been arrested for activities in Syria in the first three months of this year - already far higher than the 25 arrested last year.
Officers are working with Muslim charities and community groups nationally on the new campaign. And they are distributing a leaflet in the shape of a passport warning Britons about the dangers of travelling to Syria.