IS hostage murderer Abu al-Umarayn killed in US air strike

Abdul-Rahman Kassig founded an aid group that delivered supplies to Syrian refugees

Islamic State (IS) militant Abu al-Umarayn, who murdered several Western aid workers, has been killed in an air strike in Syria, the US says.

Coalition forces had conducted "precision strikes" on Sunday against IS leaders in south-east Syria, including Umarayn, the military said.

The militant was believed to be responsible for beheading US aid worker Abdul-Rahman Kassig in November 2014.

An ex-US Army ranger, Kassig was known as Peter before converting to Islam.

US Central Command (Centcom) confirmed on Monday that "several" members of IS were killed in Syria's Badiyah Desert.

Centcom singled out Umarayn for "posing an imminent threat to coalition forces" and said he was "involved in the killing of American citizen and former US Army Ranger, Peter Kassig" as well as several other Western hostages.

• An idealist 'simply trying to help'

• Abdul-Rahman Kassig in his own words

The 26-year-old founded a humanitarian organisation in 2012 to help refugees who had fled from Syria.

In a letter from that year, he wrote: "The truth is sometimes I really think I would like to do something else, but at the end of the day this work is really the only thing that I have found that gives my life both meaning and direction."

Abdul-Rahman Kassig, known as Peter Kassig before his conversion, was beheaded in 2014

He was captured by IS in 2013 en route to Deir Ezzor in eastern Syria.

The following year, he was shown being beheaded in a video released by the group - the fifth Western hostage to be murdered by IS members.

Then-President Barack Obama described the murder as "an act of pure evil".

His parents, Ed and Paula, from Indiana, said at the time they were heartbroken by his death. and vowed to "work every day to keep his legacy alive as best we can".

Abdul-Rahman (aka Peter) Kassig

• Former US Army Ranger

• Served in Iraq in 2007

• Travelled to Lebanon in May 2012, volunteering in hospitals and treating Syrian refugees

• Founded aid organisation Special Emergency Response and Assistance (Sera) in 2012 to provide aid to Syrian refugees

• Captured by Islamic State in October 2013 while travelling to Deir Ezzour in eastern Syria

• Converted to Islam in 2013, changing name from Peter Kassig

Islamic State has lost nearly all the territory it once controlled, spanning Syria and Iraq.

At the peak of the group's power, about 10 million people lived in IS-controlled areas, but the US military said earlier this year that the jihadists had been ousted from 98% of their former territory.

The US-led coalition is supporting Kurdish and Arab militias fighting to oust IS fighters on the border with Iraq.