UPDATE, June 27, 11:50 a.m. EDT: The British Foreign Office said Saturday at least 15 of the 39 people killed in Friday's terrorist attack on a resort in Sousse, Tunisia, have been identified as British nationals, Reuters reports.

Original story begins here:

British Prime Minister David Cameron said many of those killed by a gunman disguised as a tourist at a Tunisian hotel Friday were his compatriots, based on his discussion with Tunisia’s President Beji Caid Essebsi. At least 39 people were slain and dozens wounded by Seifeddine Rezgui, 23, in the attack in the coastal resort town of Sousse. The Islamic State group claimed responsibility for the massacre.

“We are working with the Tunisian authorities to identify a final number on the British casualties, but I’m afraid that the British public need to be prepared for the fact that many of those killed were British,” the U.K. prime minister said in a statement Saturday.

Cameron denounced the terrorists responsibile for the attack and said they ultimately would be unsuccessful in achieving their aims:

“For as much as they try to divide people around the world, they will only unite us more strongly in our determination to defeat these Islamist extremists and all that they stand for. We will keep working with our partners around the world. it will take time, vigilance and determination. But there is no place for these Islamist extremists in the modern world, and we will defeat them.”

Among the dead are Lorna Carty, an Irish nurse in her 50s who was celebrating her husband Declan’s recovery from heart surgery, and Carly Lovett, 24, a recently engaged British beauty blogger, the Guardian newspaper in the U.K. reported. Tunisia’s health ministry indicated eight of the dead have been identified as British, one as Belgian and one as German, BBC News said.

The attack Friday began around noon local time when Rezgui, a former aviation student at a university in Kairouan, about 40 miles east of Sousse, pulled out a Kalashnikov assault rifle and started shooting tourists. He was shot dead by  police. The Islamic State group claimed responsibility for the attack in what it called a “den of vice,” BBC News reported.