PHOENIX (AFP) - US President Barack Obama on Friday expressed his condolences to the parents of American hostage Kayla Mueller, who died while held by the Islamic State group.

The White House said Obama met Carl and Marsha Mueller, parents of Kayla Mueller as well as her brother during a visit to a Phoenix military veterans' hospital.

Islamic State in Iraq and Syria (ISIS) fighters claimed Mueller, who was seized in the Syrian city of Aleppo in August 2013, was killed in a Feb 6 coalition air strike that buried her in rubble.

US officials have said the circumstances of the 26-year-old aid worker's death remain unclear.

The girl's father has expressed strong reservations about the longstanding US policy of refusing to negotiate with or pay ransom to foreign groups that have kidnapped Americans.

"We understand the policy about not paying ransom," Carl Mueller said after his daughter's death.

"But on the other hand, any parents out there would understand that you would want anything and everything done to bring your child home. And we tried. And we asked. But they put policy in front of American citizens' lives."

The White House gave few details about Friday's meeting.

"The Muellers live in Arizona, so this was an appropriate occasion for the President to visit with them," said spokesman Eric Schultz.

"The President expressed his and the First Lady's condolences for Kayla's death.

"He appreciated the chance to hear from the Muellers more about Kayla's compassion and dedication to assisting those in need around the world."