Hundreds of Britons are thought to have gone to Syria over the last few years to join arms in the bloody battle against the Syrian government. UK police made an unprecedented appeal calling on Muslim women to urge their relatives not to join the conflict following a number of deaths of British men on Syria's battlefields. Counter-terrorism officers warned that young, idealistic men were in danger of being radicalized and aspiring terrorists may be travelling to Syria for terror training. Some 40 Syria-related arrests were made in the first three months of this year, up from 25 in the whole of last year, and Scotland Yard warned that Britons caught fighting in Syria were crossing a "red line" and would be investigated. But there are fears that women joining their husbands in terrorist groups to try to oust the Syrian government may inadvertently be helping him stay in power as they clash with other factions trying to depose him, the Daily Mirror said. The newspaper claimed that 10 British women - two teenagers from Portsmouth, two women from London, another from Surrey and five from cities in the north of England - had travelled to join the war. It is believed they may have linked up with the rebel group Islamic State of Iraq and the Levant (ISIL), which is so violent it has reportedly been disowned by al-Qaeda. Shiraz Maher, an expert in radicalization from Kings College London, told the Mirror: "Most British jihadists go to Syria for sincere reasons to help in what they believe is a struggle against oppression but many don't appreciate the reality on the ground. "There are around 10 British women out there, we believe, and most have travelled to Syria with their husbands.” Around 400 Britons are believed to have gone to Syria over the last two years, authorities believe, with an estimated 20 having died. Among them is 18 year-old Abdullah Deghayes, from Brighton, who is believed to have died in Kassab, in Latakia province, earlier this month after leaving the UK in January. His aunt, Amina Deghayes, questioned Thursday's announcement, saying it failed to provide a concrete solution to the problem of young men flocking to fight in the civil war. She warned that families are already urging their loved ones not to fight, but too often their appeals fall on deaf ears. 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. Officers are working with Muslim charities and community groups nationally on the new campaign. They are also distributing a leaflet in the shape of a passport warning Britons about the dangers of travelling to Syria.