Fifteen Britons have died following the attack on a Tunisian beach resort, the Foreign Office has confirmed.
But Foreign Office minister Tobias Ellwood warned the death toll was likely to rise.
He said it was “the most significant terrorist attack on British people” since 52 people were killed in the London 7/7 bombings in 2005.
A Tunisian student linked to Islamic State carried out the gun attack on a beach near Sousse which killed 38.
None of the identities of the British fatalities has been officially released.
Carly Lovett, 24, from Gainsborough in Lincolnshire, Lisa Burbidge, in her 60s, from Tyne and Wear, Adrian Evans, 44, from the West Midlands and his 22-year-old nephew Joel Richards, and Bruce Wilkinson, 72, from Goole in Yorkshire are among the dead, according to sources.
Couple Sue Davey and Scott Chalkley, 42, was also killed, according to their respective sons. Ms Davey’s son Conor Fulford and Mr Chalkley’s son Ross Naylor both confirmed the deaths on Twitter, where they had made appeals to find them after the attack.
An Irish national was also among the dead. She was named locally as Lorna Carty, who was in her 50s and from Robinstown in County Meath.
The Tunisian authorities said one Belgian and one German citizen had been identified among the dead, while Tunisians and French are also thought to have been victims.
Mr Ellwood said the death toll was likely to rise because several people had been “seriously injured in this horrific attack”.
Prime Minister David Cameron called the attack on the beach “savage”.
People gathered in Sousse on Saturday night for a protest against terrorism.
Crowds gathered after dark with some holding candles and others carrying flags, including those of the UK and Tunisia.