London, Dec 4 (IANS): Islamic State (IS) fanatics have identified Britain as their next target, a security expert has warned.

British-born jihadis who have travelled to Syria to join the extremist group have been tasked with returning home to carry out a Paris-style terror attack within weeks, the Daily Mail reported on Friday.

European security agencies have reportedly obtained "specific intelligence" that Britain is next on the IS' hit list, with the risk heightened in the wake of the Commons vote on Wednesday which saw a majority of MPs back airstrikes on the terrorists' strongholds in Syria.

Five Royal Air Force (RAF) Tornado jets carried out first airstrikes in Syria on Thursday. It targetted IS positions in the conflict-ridden country.

CNN terrorism analyst Paul Cruickshank said he had spoken to an unidentified 'senior European counter-terrorism official' who received intelligence that IS is "aiming to hit the United Kingdom next".

"The intelligence suggests that British IS operatives in Syria and Iraq are being tasked to return to launch an attack against the UK," Cruickshank said.

"They are treating this very, very seriously indeed" he said, adding "however it is not clear how imminent this threat is."

The number of Britons who have fled the country to fight for IS has hit 800. A latest defence ministry review said up to 400 are now back .

"A large proportion were previously unknown to the police and security agencies," the report said. 

"Some of these, and many of those who remain in Syria, pose a threat to our security."