British nationals have been warned to stay away from Kurdistan as American bombers begin to pound Islamic State positions in northern Iraq.
The Foreign Office has issued fresh travel advice as Iraq and the United States launches sir-strikes in response to the Islamic State's threats to massacre Iraqi minority groups.
Thousands of people have already fled from heavily armed jihadists, with up to 40,000 members of the Yazidi sect seeking refuge up a mountain.
Many others, including thousands of Christians, have taken refuge in Kurdistan – which is semi-autonomous from Iraq and where the Islamic State (formerly known as Isis) has opened a new front in recent weeks.
Sunni fighters from the Islamic State, an al Qaeda-offshoot bent on establishing a caliphate and eradicating unbelievers, have swept through northern Iraq since June. Their advance has dramatically accelerated in the past week when they routed Kurdish troops near the Kurdish autonomous region in the north.
Members of the Islamic State - including at least 200 British nationals - regularly torture and execute victims for refusing to convert to Islam. They then brag about it on social media with grisly images.
The Foreign Office has advised British nationals not to travel to the provinces of Salah-ad-Din and Diyla in Kurdistan.
Any Britons in the provinces of Ebril, Sulaymani and Dohuk should leave at once, warned the British government.
The advice comes as American airstrikes hit areas near Kurdistan currently occupied by Islamic State militants.
Britain has joined American efforts to halt the Islamic State's advance by providing surveillance and refuelling.
Prime Minister David Cameron has spoken of a moral duty to help Christian groups being threatened by Muslim radicals. Food parcels are to be dropped by air for people currently cut off from help by Isis.