On Sunday, five Iran-backed fighters were killed in an airstrike in eastern Syria near the border with Iraq the Syrian Observatory for Human Rights (SOHR), a U.K.-based war monitor reported.

The head of SOHR, Rami Abdul Rahman said that the airstrike targeted three military vehicles belonging to Iran-backed paramilitary fighters near the Iraqi border town of Albu Kamal. The Observatory said that military reinforcements for Iranian militias and their allies had arrived in the area just days before.

While the Observatory did not specifically state who conducted the airstrike, Rahman said that, “Israel was likely responsible.”

Sky News Arabia had earlier reported that unidentified aircraft carried out the pre-dawn airstrike and that the targets of the bombing were Iranian-backed proxy forces.