A spokesman for the US-led coalition said a senior Daesh militant involved beheadings of an American and other Western hostages was killed in Syria.
The US-led coalition in Syria said on Monday it killed a senior Daesh member involved in the killings of an American aid worker and other Western hostages.
Abu al Umarayn was accused of involvement in the November 2014 beheading of Peter Kassig, a former US ranger who was doing volunteer humanitarian work when captured in 2013.
"He was killed and more information will be available after a full assessment," Sean Ryan, spokesman for the US-led coalition, said in a statement issued after the Sunday strikes.
"Al Umarayn had given indications of posing an imminent threat to coalition forces and he was involved in the killing of American citizen and former US Army Ranger, Peter Kassig," he said.
Ryan said that Umarayn had also been involved in the killing of several other prisoners.
It is the first time the coalition, which has been hunting down Daesh in Iraq and Syria since 2014, has announced the killing of a Daesh leader linked to Kassig's death.
At the time of the killing, Daesh released a video showing Kassig's severed head but did not publish footage of the decapitation, as it had done for other hostages.
The Syrian regime's media outlet SANA had earlier on Sunday accused the US-led coalition of firing on its positions in remote eastern regions.
"The American coalition forces launched around 8:00 pm (1800 GMT) this evening several missiles against some positions of our forces in the Ghorab mountains south of Sukhna," SANA said.
Quoting a regime source, it said the bombardment had caused only material damage.
The Syrian Observatory for Human Rights said US-led forces fired "more than 14 missiles" at a regime forces convoy as it was passing through the desert.
"The group was lost in the middle of the desert around 35 kilometres from the Al Tanf base", said the Observatory's director Rami Abdel Rahman.
The United States often uses this base to launch its strikes against Daesh.
Coalition spokesman Sean Ryan denied any strikes targeted Syrian regime forces.
"False, the strikes were as the report stated and directed at ISIS [Daesh]," he said, using another acronym for the group.
Kassig founded a humanitarian organisation in 2012 that trained some 150 civilians to provide medical aid to people in Syria.
His group also gave food, cooking supplies, clothing and medicine to the needy.
He took the name Abdul Rahman after converting to Islam.
His killing was part of a gruesome series of Western hostage beheadings that Daesh filmed and published to shock the world as it attempted to expand across the region.
Before Kassig's decapitation, which Daesh announced on November 16, four other hostages were killed by Daesh:
- British aid worker Alan Henning (video released on October 3)
- British aid worker David Haines (video released on September 13)
- US journalist Steven Sotloff (video released on September 2)
- US journalist James Foley (video released on August 19)
Another hostage held at the time and whose killing was threatened was British journalist John Cantlie.
He later appeared in videos in which he uttered Daesh propaganda but, more than six years after his kidnapping, his fate remains unclear.
The leader of the cell which was responsible for the killings and became known as "The Beatles" was believed to be Mohammed Emwazi, a British militant nicknamed "Jihadi John" who was killed in a drone strike in 2015.
After expanding to control a so-called "caliphate" straddling Syria and Iraq which was larger than Britain, Daesh suffered a string of military setbacks.
It has virtually no fixed positions left in Iraq and is now defending a few pockets in desert areas of Syria, including the region where Sunday's strikes were carried out.
The coalition as well as the Syrian regime and its Russian backers have all repeatedly vowed to carry on the fight until achieving a full victory over Daesh.