A global watchdog said chemical weapons may have been used in air strikes by Syrian government loyalists near Palmyra, in an area controlled by the Islamic State (IS) group.
"The allegations regarding the use of chemical weapons in the area of [Oqayrabat], in the Hama governorate in Syria, reported by the media recently are of serious concern," the Organization for the Prohibition of Chemical Weapons said on December 13.
At least 53 civilians, including 16 children, were killed on December 12 in air strikes targeting IS-held Oqayrabat and a string of villages nearby, according to the British-based Syrian Observatory for Human Rights.
Observatory head Rami Abdel Rahman said there were cases of suffocation but he could not confirm accusations of a chemical attack.
The strikes came a day after IS took back control of the ancient desert city of Palmyra, in the neighboring province of Homs.
A United Nations investigation has determined that Syrian government forces carried out three chlorine gas attacks on villages in 2014 and 2015.
It also found that IS was behind a mustard gas attack in Syria in August 2015.
Based on reporting by AFP and TASS