Islamic State aid hostage, Kayla Mueller, confirmed dead

US President Barack Obama confirmed the death of Kayla Mueller, a US aid worker who had been held hostage by Islamic State militants, saying the United States would “find and bring to justice the terrorists who are responsible”.

Mueller’s family said they were “heartbroken” to learn of her death and released a copy of a letter she wrote in 2014 while in captivity.

The comments by Obama and the family came four days after Islamic State said Mueller, a 26-year-old humanitarian worker from Arizona, was killed when Jordanian fighter jets bombed a building where she was being held, although Jordan expressed doubt about the Islamist militant group’s account of her death.

Mueller was determined to have died after her Islamic State captors privately contacted her family over the weekend, a White House spokeswoman said.

“Over the weekend, the family received a private message from Kayla’s ISIL captors containing additional information,” National Security Council spokeswoman Bernadette Meehan said, using an acronym for Islamic State.

“Once this information was authenticated by the intelligence community, they concluded that Kayla was deceased,” Meehan said.

US officials said they had no evidence to support Islamic State claims that she was killed in a Jordanian air strike, adding the details surrounding her death were unclear. Mueller was the last-known US hostage held by Islamic State, which controls wide areas of Syria and Iraq. She was taken hostage in the northern Syrian city of Aleppo in August 2013.

The group has beheaded three other Americans, two Britons and two Japanese hostages, most of them aid workers or journalists, in recent months.

Meanwhile, Syrian president Bashar al-Assad said third parties including Iraq were conveying information to Damascus about the US-led campaign of air strikes against the Islamic State militant group in Syria.