American aid worker Kayla Mueller - who was being held by Islamic State - has died, President Barack Obama has confirmed.
Ms Mueller's family said they were "heartbroken" at the news, and released a copy of a letter she had written in captivity.
Confirmation of Mueller's death comes days after Islamic State claimed the 26-year-old had died in a Jordanian air strike.
David Cameron says he is "deeply saddened" to learn of the death of US hostage Kayla Mueller, claiming her "brutal" Islamic State captors are responsible.
“I am deeply saddened to hear of the death of US aid worker Kayla Mueller and my thoughts are with her friends and family as they deal with this awful news," the prime minister said.
“Let me be clear – those responsible for her death are the terrorists that kidnapped Ms Mueller and who held her against her will ever since.
"Kayla travelled to the region to help men, women and children forced to flee their homes and her death demonstrates yet again the indiscriminate brutality of ISIL.
"We will work with coalition partners to ensure her murderers face justice, however long it takes."
Following confirmation of the US hostage's death, Kayla Mueller's family have released a copy of a letter she wrote in captivity in 2014.
Here is what we know about American aid worker Kayla Mueller who was being held by Islamic State.