Thousands of foreign tourists have applied to tour companies to evacuate Tunisia as the country was hit by the vicious attack that left 39 tourists dead in summer resort town of Sousse."I'm afraid that the British public need to be prepared for the fact that many of those killed were British," British Prime Minister David Cameron told reporters, as five were already confirmed dead. Tunisia's Prime Minister Habib Essid earlier said that most of the dead were Britons. The process of identification was taking time because the victims were not carrying documentation with them on the beach, the Tunisian authorities said.German and Belgian tourists were among other casualties in the attack on Friday at the Imperial Marhaba hotel in Sousse, 140 km (90 miles) south of the capital Tunis.Tour operators Thomson and First Choice, which are owned by German travel group TUI, said they had about 6,400 customers across Tunisia at the time of the attack, including several of the people killed and injured.They sent 10 planes to evacuate tourists and said 1,000 had already been repatriated, and a total of 2,500 tourists will be repatriated as of Saturday. They also said they would cancel all their holiday packages to Tunisia for at least the next week. On Friday night, 13 aircraft took off from Enfidha Airport north of Sousse, carrying tourists back home.A gunman disguised as a tourist opened fire on tourists as they lounged on the beach at the hotel, with a rifle he had hidden in an umbrella.The attack took place during the holy Muslim month of Ramadan, on a day in which a decapitated body daubed with Arabic writing was found in France, a suicide bomber killed two dozen people at a mosque in Kuwait and at least 145 civilians were reported killed by ISIS militants in northern Syria.Prime Minister Essid said that Tunisia planned within a week to close down 80 mosques that remain outside state control for inciting violence.It was the second big attack in Tunisia this year following the assault on the Bardo Museum in the capital in March, when the gunmen killed 21 foreign visitors.Tunisia, which has undergone a largely peaceful transition to democracy since its 2011 Arab Spring uprising, depends heavily on foreign tourism and the violence is bound to be a severe blow to the industry. Tourism accounts for seven percent of Tunisia's GDP and almost 400,000 direct and indirect jobs.Essid on Saturday announced that from next month armed tourist security officers would be deployed all along the coast and inside hotels.But a heavy blow had already been delivered to the key industry with British tour operator Thomas Cook announcing it would offer all customers the possibility to change bookings to the North African country up to and including July 24.The tour operators said they had sent trauma specialists to Sousse to help. "We had situations where people were so frightened that they locked themselves in their rooms...We are doing everything we can to help our customers and ensure we help them through this very difficult period and bring them home safely," Peter Long, chief executive of TUI's British arm, told a news conference.The tour operators said they were working closely with the local authorities to confirm the exact details of casualties.