* European countries fear return of radicalised fighters
* Hundreds of Britons thought to have gone to Syria
* Syria-related terrorism arrests increased this year (Updates after police briefing, adds background)
By Michael Holden
LONDON, April 24 (Reuters) - British police are asking Muslim women to dissuade young people in their communities from going to fight in Syria, the latest tactic by a European government worried about the security risk posed by youths radicalised by war.
Governments estimate that several thousand Europeans have gone to Syria since the war against President Bashar al-Assad started three years ago. The Dutch said this week that dozens of its citizens had been radicalised in Syria, and France announced its own measures to counter the phenomenon.
"I have been very concerned indeed to see the number of young people who have been travelling to Syria," Helen Ball, Britain's National Coordinator for Counter Terrorism Policing, told reporters after meeting 40 women from a variety of organisations at the launch of the new campaign.
She said the aim was to see how women could challenge the motivations of young Muslims, mainly men, from going to Syria be it to fight or to deliver aid and "possibly becoming radicalised and becoming an even greater threat".
Since the 2001 attacks on New York and Washington, Britain, home to about 2.7 million Muslims, has been fearful of its nationals travelling to militant training camps abroad, and then posing a potential security risk at home.
That concern increased after four young British Islamists, two of whom had been to al Qaeda camps in Pakistan, killed 52 people in suicide bomb attacks on London in July 2005.
In February, Islamist fighters released a video of what they said was a British man carrying out a suicide bombing on a prison in Aleppo, and, just last week, a teenager from southern England was the latest to be reported killed in fighting.
"We know that the issue of Syria is held as a grievance amongst mainly Muslim youth. It is something that they feel they want to do something about," said Sajda Mughal, from the JAN Trust charity which works with disadvantaged Muslim women.
"It's the mothers who are the ones who need to be protecting their child in order for them not to travel out to Syria," added Mughal, who narrowly escaped serious injury herself in the 2005 London bombings.
Among the policies France unveiled this week to stop its citizens joining the civil war, was the possibility of stripping people of French nationality, along the lines of British legislation introduced last year.
It is also encouraging parents to alert officials to suspicious behaviour in their children via a new hotline.
In London, Ball said the police recognised that not all who went to Syria did so to fight, and said the campaign also aimed to inform people how they could help those in need in Syria "safely and legally".
However, she made it clear that those who did engage in combat risked arrest back in Britain - something that is becoming increasingly common.
About 40 people were detained in the first three months of this year, mostly on suspicion of terrorism offences, compared with just 25 during the whole of 2013.
One of those was former Guantanamo Bay prisoner Moazzam Begg who was charged in March with terrorism offences, although his supporters say he was merely carrying out humanitarian work.
Consequently, some British Muslims view the latest police-led initiative with a great degree of scepticism, although Ball said they would not share concerns raised by anxious families with the British intelligence agency MI5.
"We view this as a duplicitous attempt by the police to exploit the natural anxiety of mothers in the Muslim community to assist them in their counter-terrorism work," said Asim Qureshi, Research Director at CAGE, a charity which campaigns for those detained on terrorism charges. (Editing by Robin Pomeroy)
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