US woman held hostage by IS confirmed dead

The US has confirmed the death of aid worker Kayla Mueller, who was held hostage by the Islamic State (IS) terrorist group after being captured in Syria, media reported Tuesday.

"We are heartbroken to share that we've received confirmation that Kayla Jean Mueller, has lost her life," a statement from the family read.

"Kayla was a compassionate and devoted humanitarian. She dedicated the whole of her young life to helping those in need of freedom, justice, and peace," the family said, CNN reported.

President Barack Obama offered his condolences to the young woman's family and vowed to "bring to justice the terrorists who are responsible". Mueller "represents what is best about America", he said.

On Friday, IS claimed that Mueller -- captured in northern Syria in 2013 -- had been killed in a building that was hit during a Jordanian airstrike on Raqqa, the militants' de facto capital in Syria. At the time, IS offered no proof to back up its claim, other than an image of a badly damaged building.

Over the weekend, the IS sent the family a private message, National Security Council spokesperson Bernadette Meehan said Tuesday.

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

The new information does not clarify how Mueller died, a law enforcement source familiar with the case said on condition of anonymity.

Mueller's relatives Tuesday also released a handwritten letter that they say she wrote while in captivity in spring 2014.

Mueller fell into the hands of hostage-takers in August 2013 in Aleppo, Syria, her family said, after leaving a Doctors Without Borders hospital.

Her family said IS contacted them in May with proof that she was alive. The militants eventually said they would kill her if the family didn't pay nearly $7 million by Aug 13, according to a source close to the family.