BEIRUT (AP) — Syrian opposition activists say unknown warplanes have targeted an arms depot belonging to Iranian-backed militias in the eastern Syrian town of Boukamal, near the Iraqi border.

The Britain-based Syrian Observatory for Human Rights says the airstrikes began late Sunday and continued after midnight, killing 18 Iranians and pro-Iranian fighters. They also caused extensive damage to the depot and vehicles.

Two local activist collectives in eastern Syria — the Euphrates Post and the Sound and Pictures — also reported the airstrikes in Boukamal, without giving a death toll.

The Sound and Pictures says the strikes hit an arms depot for Iraq's Popular Mobilization Forces, a mostly Iran-backed Shiite militias.

Israel views Iran as its greatest threat and has allegedly struck Iran-linked targets as far away as Iraq in recent weeks.