The Foreign Office on Friday urged Britons in the Arbil, Sulaimaniyah and Dohuk provinces of Iraq's autonomous Kurdistan region to "leave now" following attacks by extremists.
The travel advice, which was issued before US jets struck jihadist positions near the city of Arbil, does not extend to the Kurdish capital itself, an spokeswoman said.
In an updated guidance, the Foreign Office advised against all travel to those areas of the Kurdistan region affected by fighting following attacks by jihadist militants this week.
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"If you're currently in these areas you should leave now," it said.
The Foreign Office also advised against all travel to Anbar, Nineveh, Salah Al-Din and Diyala provinces and all of the area south of Kirkuk City limits.
"Those British nationals already present in the Kurdistan region should take precautions to remove themselves from areas close to the conflict," it said, warning that the situatikon could "deteriorate quickly".
For the rest of Iraq, London advises against all but essential travel.