The US-led coalition against the Islamic State group said on Monday that it had killed a senior jihadist involved in the executions 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.
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"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.
The spokesman said the jihadist had also been involved in the execution of several other prisoners.
It is the first time the coalition, which has been hunting down Isil fighters in Iraq and Syria since 2014, has announced the killing of a jihadist leader linked to Kassig’s death.
At the time of the execution, Isil released a video showing Kassig’s severed head but did not publish footage of the decapitation, as it had done for other hostages.
Syria’s official SANA news agency had on Sunday accused the US-led coalition of firing on Syrian army 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," causing only "damage to equipment," Sana said, citing a military source.
According to the monitoring Syrian Observatory for Human Rights, coalition forces positioned in the Al-Tanf region fired "more than 14 missiles" at a Syrian army convoy as it was passing through the desert in the far east of Homs province.
"The group was lost in the middle of the desert around 35 kilometres from the Al-Tanf base" of US and British troops, the Observatory’s director Rami Abdel Rahmane told AFP.
The United States generally uses this base to launch its strikes against Isil jihadists. It has also been used in the past to train Syrian opposition fighters.
Peter 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.
Before Kassig’s death, his life had been threatened in an earlier video showing the beheading of another aid worker, Briton Alan Henning.
Kassig’s mother Paula reached out directly to Isil militants to plead for her son’s life.
The international coalition intervened in Syria and Iraq in 2014 to fight the expansion of Isil after it had taken control of vast swathes of territory straddling the two countries.
Defeated in Iraq, the group still retains territory in some parts of the Syrian desert, particularly in the east of the country, where the coalition continues to fight the jihadists with the support of an alliance of Kurdish and Arab fighters.