Britain says Islamist militants 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.
UK home secretary Theresa May, the interior minister, said she would chair a meeting of the government's Cobra emergency response committee on Sunday to ensure the government's response to events in Tunisia was adequate.
She said she had not seen evidence Islamist militants had specifically targeted British tourists in Friday's attack in the Tunisian resort of Sousse.
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, May said the number of Britons confirmed killed in the attack was expected to rise. Many Britons were due to fly home from Tunisia on Sunday, having cut short their holidays.
In Britain, the threat level from international terrorism remains at "severe", its second-highest setting, meaning an attack is highly likely. May said authorities had thwarted 40 attacks in the last decade and "a number of plots" in recent months.