BEIRUT - Nearly 40 foreign fighters allied to Syria's regime were killed in an overnight bombing raid near the country's eastern border with Iraq, a monitor said on Monday.
The Britain-based Syrian Observatory for Human Rights said the strike was one of the deadliest on forces allied with Syria's government.
"Thirty-eight non-Syrian fighters from regime loyalist militias were killed in the night-time raid on Al-Hari, on the Syrian-Iraqi border," said Observatory head Rami Abdel Rahman.
Syrian state media reported the attack overnight, citing a military source and accusing the US-led coalition fighting the Islamic State group of carrying it out.
It said several people were killed and wounded but did not give a specific number.
The coalition did not respond to requests for comment, and the Observatory could not immediately identify who carried out the Al-Hari attack.
US-backed fighters and Russia-supported regime forces are carrying out separate operations against small pockets of IS-held territory in Syria's eastern Deir Ezzor province, where Al-Hari lies.
Both sides have mostly avoided running into each other and a de-confliction line exists to avoid such incidents, but there have been exceptions.
In May, a dozen pro-regime fighters were killed in an air strike on Syrian army positions that the Observatory and Syrian state media said was carried out by the coalition.
The Pentagon denied responsibility.
Deadly clashes also broke out in April, but the bloodiest incident yet was in February, when the US-led coalition carried out air strikes that killed at least 100 pro-regime fighters in eastern Syria.