A suicide bomber detonated an explosive vest on a bus in Syria near the Atmeh border crossing into Turkey late on Sunday, killing at least 15 people and injuring 25 others, some critically, the Syrian Observatory for Human Rights said.

The bus was carrying fighters for Syria's civil war, the observatory reported.

Pictures circulating on social media showed the burnt out remains of a bus and medics treating injured people.

The sources reported that the explosion took place at the entrance of Atmeh refugee camp in Syria, located just across from the Turkish border town of Reyhanlı.

The injured people were transferred to nearby hospitals while those who were in severe condition were brought to Turkey for treatment.