At least five Britons are among the 37 killed in Tunisia after a gunman dressed as a beachgoer opened fire, the Foreign Office has said.
Foreign Secretary Phillip Hammond said the British death toll could yet climb higher following the midday massacre on Friday, that occurred between the Soviva and Imperial Marhaba Hotels in the seaside town of Sousse, a popular holiday destination for Britons.
A "high proportion" of the casualties are expected to be be from the UK, he said, according to the BBC.
An injured woman is carried away from the scene
James McGuire, 60, was among the dead, the Mail Online reported. The website said Matthew James, 30, from Cardiff, was also fighting for his life after being shot four times in the stomach.
Mail Online spoke to James' fiancee, Sarah Wilson, who said her partner had saved her life, gallantly throwing himself "in front of me" when the shooting started, before telling her to run away, and to "tell our children that their daddy loves them".
Wilson said it was the "bravest thing I've ever known".
In the immediate aftermath of the attack, Interior Ministry spokesman Mohammed Ali Aroui said one gunman had been killed in a firefight with security forces at the scene, while another had fled. It was later reported than the gunman had acted alone, although police were said to have arrested another suspect near a motorway some time later.
At least 36 people were wounded in the rampage.
Meanwhile, the final moments of the gunman's death march, have been detailed, with chilling images emerging showing him prowling the streets in the hunt for further victims.
Tunisia's Secretary of State for Security, Rafik Chelly, said the mass-murderer is a local student who was previously unknown to authorities.
He said: "He went to the beach, dressed like someone who is going for a swim and he had a parasol (sun umbrella) inside which he had his weapon. After he arrived at the beach, he used his weapon."
It is thought the shooter used a boat and a jet ski to access the beach.
Prime Minister David offered 'our solidarity in fighting this evil of terrorism', adding: 'Our hearts go out to the victims of appalling terrorist acts in France and Tunisia.'
Details about the nationalities of the victims were scare in the aftermath of the shooting, but during the holy month of Ramadan Tunisia's Muslim population is less likely to go the beach, so those there would have been predominantly foreign tourists.
Local radio has said those killed in the resort of Sousse were mostly German and British. An Irish woman in her 50s.
Police were seen detaining this man in the aftermath of the attack
British tourist David Schofield told Sky News that he was by the pool when he heard "quite a large explosion".
"We heard people saying there were guns on the beach. People were shooting on the beach. People are running around the hotel. No-one has really been told what to do."
Susan Rickets told the channel she heard what sounded like machine gun fire.
Images are circulating online showing a grey-haired man lying face down on a beach in his swimming shorts with blood seeping from an apparent head wound. Next to him lies the body of a woman, covered by a towel. Empty sunloungers can be seen behind them.
Footage shot in the aftermath shows people hurrying to help an injured woman from her sunlounger, gently lifting her off and carrying her to safety.
Elizabeth O'Brien, an Irish woman on holiday with her two sons in the resort, described how she grabbed her children and ran for their lives when they heard gunfire erupting from one of the hotels.
"We were on the beach, my sons were in the sea and I just got out of the sea. It was about 12 o'clock and I just looked up about 500 metres from me and I saw a (hot air) balloon collapse down, then rapid firing, then I saw two of the people who were going to go up in the balloon start to run towards me - because I thought it was fireworks," the Dubliner told RTE Radio.
"So, I thought 'oh my God, it sounds like gunfire', so I just ran to the sea to my children and grabbed our things and as I was running towards the hotel, the waiters and the security on the beach started saying 'run, run run!' and we just ran to our room, which is like a little bungalow."
No one yet has taken responsibility for the attacks, though Tunisia has been on high alert since March when Islamist militant gunmen attacked the Bardo museum in Tunis, killing seventeen tourists and two Tunisians.
Sousse is a city on the east coast of Tunisia, about 87 miles (140km) south of the capital, Tunis. Around 1.2 million tourists visit Sousse every year, drawn by the hotels, sandy beaches and culture. Indiana Jones action film Raiders of the Lost Ark was filmed in the city in 1981.
Holidaymakers on the beach under attack (file picture from 2013)
Thomas Cook, which has holidaymakers in the resort, said: "Thomas Cook has been advised of an incident that occurred earlier today in Sousse, Tunisia.
"At this time, details are not clear as to which property(ies) have been affected, with conflicting news reports.
"We are currently gathering information and will provide an update as soon as possible. Our teams on the ground are offering every support to our customers and their families in the area.
"We will continue to monitor the situation, working closely with the FCO and local authorities."
It comes on the same day a man was decapitated and an Islamist flag was raised at a factory in the French town of of Saint-Quentin-Fallavier between Lyon and Grenoble. In Kuwait, a suicide bomber killed at least 25 people at a Shia mosque.
British Prime Minister David Cameron says the government's crisis committee, COBRA, will meet on Friday in response to the attacks in France and Tunisia.
He offered condolences and "our solidarity in fighting this evil of terrorism."
"The people who do these things, they sometimes claim to do it in the name of Islam," Cameron said. "They don't. Islam is a religion of peace."
He said the attackers acted from "a twisted and perverted ideology we have to confront with everything we have."