A monitor says Islamic State (IS) militants executed at least 17 people, including civilians, after seizing Syria's ancient city of Palmyra on May 21.
Rami Abdel Rahman, director of the Britain-based Syrian Observatory for Human Rights, said "IS executed 17 people, including civilians and loyalist fighters. At least four of them were beheaded."
"They were accused of working with the regime," Abdel Rahman said.
According to the Observatory, at least 460 people were killed in the battle for Palmyra that began on May 13.
The group on May 20 took full control of Palmyra, which is home to the UNESCO World Heritage site containing ancient ruins.
There are fears the IS militants would destroy the ruins as they did major archaeological sites on Iraqi territory.
Meanwhile, Islamic State said in a statement posted by followers on Twitter it was in full charge of Palmyra, including its military bases, marking the first time it had taken a city directly from the Syrian military and allied forces.