The Syrian boyfriend of US hostage Kayla Mueller who died in the hands of Islamic State (IS) terrorists has said she remained selfless even while she was held captive.

Omar Alkhani said he returned to Syria months after he and Ms Mueller, 26, from Prescott, Arizona, were captured at gunpoint outside a hospital, to try to secure her release by posing as her husband.

But when he and aid worker Ms Mueller came face to face while she was in a detention cell in Syria, she denied being his wife.

Had she told her captors she was married to Mr Alkhani, she might have been freed from the hands of the IS militants, he said.

The US government and Ms Mueller's family confirmed her death last week. Since then, hundreds of people have gathered to honour her in her home town and in Flagstaff, where she attended Northern Arizona University. IS claims she was killed in a Jordanian air strike.

Mr Alkhani had persuaded a string of people to let him plead for her release, but he left the room empty-handed and said he was thrown into another cell. He said he saw her face for just a few seconds when guards uncovered it to show it was Ms Mueller.

The guards told Ms Mueller that Mr Alkhani would not be harmed if she told the truth, so she apparently did to save him, rather than take the slim chance to save herself, he said.

"Since she's American, they would not let her go anyway. No sense to stay here, both of us," Mr Alkhani said. "Maybe she wanted to save me. Maybe she didn't know I came back to save her."

Mr Alkhani spoke from Turkey in one of his first interviews, telling how he met Ms Mueller in 2010 and the last time he saw her in 2013 as a prisoner of IS.

She and Mr Alkhani were taken hostage in August 2013 after leaving a Doctors Without Borders hospital in Aleppo, Syria, where he was hired to fix the internet connection.

Ms Mueller had begged him to let her tag along so she could see the suffering first hand and help, despite the dangers of travelling into the war-torn region. He said he agreed reluctantly.