LONDON (AFP) - Thousands of British tourists were being flown home on Saturday after the Tunisian beach massacre claimed by the Islamic State in Iraq and Syria, travel firms said.

Most of the 38 people killed in Friday's massacre were British, the Tunisian Prime Minister Habib Essid confirmed. The mass shooting occurred at the five-star Riu Imperial Marhaba Hotel on the outskirts of Sousse, about 140km south of Tunis.

"The majority are British," he told a news conference. "After come the Germans, then the Belgians and then other nationalities," he said, adding that there were also French among the victims.

He also revised an earlier death toll given by the health ministry from 39 to 38. An official from the ministry told AFP the previous figure had included the dead gunman who had attacked the popular beach resort of Port el Kantaoui.

Travel companies Thomson and First Choice, part of the TUI UK group, said their customers had been caught up in the massacre. "While the situation on the ground remains fluid, we have... had confirmation that a number of fatalities and injuries are Thomson and First Choice customers," said a statement issued by the companies.

The statement added that ten Thomson Airways flights would be repatriating about 2,500 Thomson and First Choice customers.

Mr Essid said reserve troops would be called up to reinforce security at "sensitive sites... and places that could be targets of terrorist attacks" after the massacre, the second against tourists in Tunisia this year.

The "exceptional plan to better secure tourist and archaeological sites" will include "deploying armed tourist security officers all along the coast and inside hotels from 1 July", he added.

The Premier also announced that a national anti-terrorism congress would be held in September and that financial rewards would be given to anyone who comes forward with information leading to the capture of any terrorists.