Syrian opposition activists say warplanes have targeted an arms depot belonging to Iranian-backed militias in the eastern Syrian town of Boukamal, near the Iraqi border.
The Syrian Observatory for Human Rights, a UK-based monitoring group, said at least 18 Iranian and pro-Iranian fighters were killed.
It was not clear who carried out the overnight strikes in and around the town of Albu Kamal.
But Israel has carried out hundreds of attacks on Iranian-linked targets in Syria during the country’s civil war.
Israel views Iran as its greatest threat and has allegedly struck Iran-linked targets as far away as Iraq in recent weeks.
The Syrian Observatory for Human Rights cited its sources as saying the unidentified warplanes had bombed bases, arms depots and vehicles belonging to Iran-backed militias in al-Hizam al-Akhdar and other areas around Albu Kamal.