Britain warns further Islamist attacks in Tunisia possible

Britain says the Islamic State of Iraq and Syria (ISIS) militant group may launch further attacks on tourist resorts in Tunisia after a gunman killed 39 people, including at least 15 Britons, in the worst assault of its kind in modern Tunisian history.

Attacks may be carried out by "individuals who are unknown to the authorities and whose actions are inspired by terrorist groups via social media," the Foreign Office said in updated travel advice on its website late on Saturday.

Britain's Defence Secretary Michael Fallon and Foreign Secretary Philip Hammond, writing in separate Sunday newspapers, said the Tunisian murders would inform Britain's defence and security this year and stiffen London's resolve to tackle what they described as the poisonous narrative of Islamist extremism.

With some British tourists holidaying in Tunisia still unaccounted for, the number of Britons confirmed killed in the attack is expected to rise. Many Britons were due to fly home from Tunisia on Sunday, having cut short their holidays.