Tunisian Prime Minister Habib Essid has said most of the victims of the Sousse beach resort carnage are British holidaymakers as authorities stepped up evacuation measures.
Though the UK Foreign Office confirmed there were only five Britons among the 38 people killed in the shooting, it had cautioned that the death toll could increase.
In a press conference, the Tunisian premier said: "The majority are British. After them come the Germans, then the Belgians and then other nationalities." He added there were French victims as well.
The Islamic State (Isis) has claimed responsibility for the attack, in which a lone gunman randomly opened fire at the European sunbathers at the resort. The suspect was shot dead by the police later.
The identities of the British nationals have not been released as yet but the Irish government has confirmed one of its citizens, Lorna Carty, who was in her 50s, was among the dead.
Prime Minister David Cameron tweeted: "I have called the Tunisian President to offer my support. We stand shoulder to shoulder in the fight against terrorism."
Meanwhile, travel firms have stepped up their efforts to evacuate more people from Tunisia following the shooting incident.
Thomson and First Choice are sending 10 flights to bring back their customers while the first batch of evacuees is set to arrive shortly.
In a statement, the companies said: "Due to this terrible tragedy, Thomson and First Choice are repatriating all our customers staying in Port El Kantaoui and Sousse this evening. Ten Thomson Airways flights are travelling to Tunisia to repatriate approximately 2,500 Thomson and First Choice customers."
"We will also be cancelling all Thomson and First Choice holidays to Tunisia for the next week."
The British embassy in Tunis has also sent an emergency team to the rampage spot to deal with the crisis as the diplomatic mission urged tourists to keep in touch with travel operators.