Up to 450 Britons have joined the ranks of extremists ISIS and could attack the UK, a Kurdish intelligence chief has claimed.
Lahoor Talabani, director of counter terrorism for the Kurdistan Regional Government (KRG), told Sky News that the offensive in the north of the country by ISIS should not be viewed as an attack only on the Iraqi government.
His comments echo those of Prime Minister David Cameron, who on Wednesday warned that Isis was plotting terror attacks on the UK and that militants returning from fighting in Iraq and neighbouring Syria now represent a greater threat than those from Afghanistan.
Mr Talabani said: "According to the intelligence we have, just Britain alone have around 400 to 450 known people fighting amongst the ranks of ISIS."
ISIS's British fighters could return to attack the UK, the Kurdish intelligence chief warned
He added that ISIS leader Abu Bakr el Baghdadi would use them to attack the UK if they survived the fighting, and the situation would get worse for the West if it does not intervene. He called for air strikes, ammunition and weaponry from the West.
Among the Britons claiming on social media to have been fighting with ISIS was Abu Rashash Britani, who tweeted that his leaders had ordered him to return to Britain.
He tweeted to another jihadist: "I my brother intend to go back to #UK under the order of our Ameer Abu Bakr Al-Baghdadi #foreignpolicy."
He also tweeted: "#usa manned & unmanned aircrafts flying over #iraq.They never learn,Bi'idnillah we will attack u from within brace yourself for another 9/11," and later: "I pray a revenge attack takes place in #uk against those enemies of #Islam n #Muslims."
The US is considering formal requests from Iraqi leaders to launch air strikes against militant positions, possibly using drones.
President Barack Obama indicated today that he does not need authorisation from Congress to take any steps over action in Iraq, top Senate Republican Mitch McConnell said.
While Obama has not fully ruled out the possibility of launching air strikes, such action is not imminent, officials said, in part because intelligence agencies have been unable to identify clear targets on the ground.
US vice president Joe Biden also discussed possible additional measures that the US could assist Iraqi forces.
Meanwhile, social media sites are reportedly being used to give would-be British jihadists travel advice to recruit them to fight in Iraq and Syria.
Extremists already in the countries are using media such as Twitter and the anonymous question and answer website ask.fm to pass on information about visas, travel money and how to avoid rousing suspicion and evade security to those wanting to join them, the Daily Mail reported.
Around 150 Australians are also thought to be fighting with militants in Syria and Iraq, raising fears of a terrorist threat if they return home, leading to the cancellation of passports on the advice of security agencies.
On Wednesday, Cameron said Britain could not afford to see the creation of an "extreme Islamist regime" in the middle of Iraq.
He told MPs at Prime Minister's questions: "I disagree with those people who those people who think this is nothing to do with us and if they want to have have some sort of extreme Islamist regime in the middle of Iraq, that won't affect us. It will.
"The people in that regime - as well as trying to take territory - are also planning to attack us here at home in the United Kingdom.
"So the right answer is to be long-term, hard-headed, patient and intelligent with the interventions that we make.
Isis overran Iraq's second city, Mosul, last week, and has also launched an assault on the country's biggest oil refinery in Baiji, north of Baghdad.
British oil giant BP has reportedly evacuated non-essential workers out of its Rumaila field in the south of the country.