Aid worker kidnapped in 2013 was imprisoned and tortured by Isis, and repeatedly sexually abused by Abu Bakr al-Baghdadi

The US military operation which resulted in the death of the Isis leader Abu Bakr al-Baghdadi was named after Kayla Mueller, the White House national security adviser said on Sunday.

Mueller, a humanitarian worker from Arizona, was imprisoned and tortured by Isis and repeatedly sexually abused by Baghdadi himself, having been kidnapped after travelling from Turkey to Aleppo in Syria in August 2013, seeking to visit a hospital.

In February 2015 it was confirmed that she had died in Isis custody at the age of 26. Isis claimed she died in a Jordanian airstrike in Raqqa. Her body has not been recovered.

On Sunday her father, Carl Mueller, told the Arizona Republic: “What this man did to Kayla – he kidnapped her. She was held in many prisons. She was held in solitary confinement. She was tortured. She was intimidated. She was ultimately raped by al-Baghdadi himself.

“He either killed her or he was complicit in her murder. I’ll let people who read this article make up their own mind how a parent should feel.”

When Kayla’s death was confirmed, Mueller’s family released a letter she sent from captivity.

“I have been shown in darkness, light,” she wrote, “[and] have learned that even in prison, one can be free. I am grateful. I have come to see that there is good in every situation, sometimes we just have to look for it.”

On Sunday her mother, Marsha Mueller, said: “I still want to know, ‘Where is Kayla?’ and what truly happened to her and what aren’t we being told. Someone knows, and I’m praying with all my heart that someone in this world will bring us those answers.”

Speaking to NBC’s Meet the Press on Sunday, the national security adviser, Robert O’Brien, said: “We finally brought justice to a man that beheaded the three Americans, two journalists and a humanitarian worker.”

He was referring to James Foley and Steven Sotloff, both freelance journalists, and Peter Kassig, a humanitarian worker, who were all killed in 2014.

When she was captured, Mueller had been visiting a hospital run by the international aid group Médecins Sans Frontières. O’Brien said she was “a humanitarian, great young American, idealistic, young girl”.

O’Brien added: “One of the things that Gen Milley, the chairman of the joint chiefs of staff, did was named the operation that took down al-Baghdadi after Kayla Mueller, after what she had suffered. And that was something that people should know.”