British authorities say they are stepping up security at events marking Armed Forces Day across the country amid a news report that officials foiled a bomb attack by the Islamic State group on a military parade in London.

The announcement follows attacks in Tunisia, France and Kuwait on Friday. The Sun newspaper said police foiled an attack on a London parade Saturday after an undercover reporter who obtained details on the plot alerted counter-terrorism officials.

Prime Minister David Cameron told reporters there will be "heightened security" at events paying tribute to Britain's military. He did not elaborate.

Police said security is also being beefed up for the annual gay pride parade in London Saturday.Britain's terrorism threat remains at "severe," the second-highest level, meaning an attack is considered highly likely.

Mr Cameron earlier said the public must be prepared for a high British death toll following the attack on a Tunisian beach resort. Tunisia's PM Habib Essid says the majority of the dead were British.

"We are working with the Tunisian authorities to identify the final number of British casualties but I'm afraid that the British public need to be prepared for the fact that many of those killed were British," he added.

So far, five Britons have been confirmed dead by the Foreign Office, but the Tunisian health ministry said eight Britons had so far been identified as being killed.

Thomson and First Choice said they were sending 10 planes to bring home 2,500 tourists on Saturday. German Chancellor Angela Merkel has spoken to Tunisia's president and pledged to step up cooperation in the fight against terrorism.

Tunisia's prime minister has called for all citizens to work together to defeat terrorism as thousands of tourists prepared to leave the North African country in wake of its worst terrorist attack ever.

"The fight against terrorism is a national responsibility," said a visibly exhausted Habib Essid at a press conference in Tunis earlier today. "We are at war against terrorism which represents a serious danger to national unity during this delicate period that the nation is going through."

He announced a string of tough measures to fight extremism, including examining the funding of organizations suspected of promoting radicalism, closing some 80 mosques outside government control and declaring certain mountainous zones military areas.

At the Imperial Marhaba Hotel where the attack took place, vans and buses were carrying away tourists on Saturday. While the hotel was not actually closing down, the tour operators had urged everyone to leave, the director said.

"We may have zero clients today but we will keep our staff," said Mohammed Becheur, adding the 370-room hotel had been at 75 percent occupancy before the attack.

Tourism is a key part of Tunisia's economy and had already fallen some 25 percent after a terrorist attack on the national museum in the capital Tunis that killed 22 people in March. "It's really sad but what can you do, for everyone, for the tourists, for the people who died, for their families," said Belgian tourist Clause Besser, as he recovered in the hospital from a gunshot wound he received fleeing from the attacker. "For me, somehow, with a bullet in the leg, it's not a catastrophe. For those who died or were injured for life, it's something else."

British travel companies Thomson and First Choice said they are flying back thousands of tourists from Tunisia Saturday and are cancelling all flights to the country in the coming week. Tourist flights from Ireland to Tunisia have continued in the wake of the attack, but travel agents are offering full refunds for those canceling.Slovakia has sent a plane to evacuate some 150 of its citizens who are currently in Tunisia, according to the Foreign Ministry and Scandinavian tour operators have stopped all flights to the North African country for the rest of the season.

The Tunisian Ministry of Health has confirmed the nationalities of 10 of the 39 victims of the attack, including eight Britons, a Belgian and a German. The government of Ireland said an Irish nurse was also among those who were killed.

Relatives and family friends say Lorna Carty was fatally shot as she sunbathed. She and her husband, Declan, had received the holiday as a present to help Declan Carty relax following his recent heart surgery. Family friends speaking to the couple's two children said Lorna Carty went ahead of her husband to the beach, where she suffered fatal gunshot wounds and was pronounced dead in hospital.