LONDON: The British government cautioned Sunday that other attacks "are possible" in Tunisia as Queen Elizabeth II sent condolences to that relatives of victims of a mass shooting that killed at least 38.
The 89-year-old monarch said she and her husband Prince Philip were "shocked" at the attack in which at least 15 British people died.
"We send our sincere condolences to the families of those who were killed and our deepest sympathy to the people who are still fighting for their lives in hospital, and those who have been seriously injured," the queen said in a statement.
"Our thoughts and prayers are with those of all countries who have been affected by this terrible event."
Interior minister Theresa May said there had been no change in the British toll, the worst in a terror attack since the 2005 London bombings, but told the BBC: "We are expecting that to rise."
Foreign Office minister Tobias Ellwood said Saturday that several British tourists had been seriously injured, while desperate families have said that some relatives were still unaccounted for.
Three Irish citizens were also killed, according to the Irish foreign ministry.
Prime Minister David Cameron announced that he had asked for flags over his office 10 Downing Street to be flown at half mast "in memory of the victims of the terrorist attack in Tunisia".
It was the largest British loss of life in a terror attack since 52 people died in suicide bombings on the London transport system on July 7, 2005.
About 20,000 Britons were on package holidays at the time of the attack, and travel companies have laid on flights to repatriate those who want to come home.
In updated travel advice, the Foreign Office urged those who remained in Tunisia to be vigilant and said there was a risk of further incidents.
"Further terrorist attacks in Tunisia, including in tourist resorts, are possible, including by individuals who are unknown to the authorities and whose actions are inspired by terrorist groups via social media," it said.
The TUI travel group, which runs Thomson and First Choice holidays, sent out 11 flights on Saturday and had another 12 planned for Sunday, with the aim of bringing home a total of 2,500 people over the weekend.
Three members of the same family were among the British victims killed, according to media reports, identifying them as 19-year-old student Joel Richards, his uncle and grandfather.
Another 39 people were injured, including 25 Britons, in the attack claimed by the Islamic State group.
The shooting came the same day as a bombing in Kuwait, which was also claimed by the IS group, and a suspected Islamist murder at a factory in France.
The British government held meetings of its emergency response committee on Friday and on Saturday, and May was due to chair a third meeting later on Sunday.