The Syrian air defences, on Tuesday night, managed to shoot down 13 "targets," as military radars detected warplanes in Syrian airspace, said the observatory, reports Xinhua news agency.

Missiles from Syrian air defence systems continued to be launched toward "targets" over the sea rather than on land, the Britain-based war monitor added, noting that it is still unclear whether the targets were missiles or drones.

There were no immediate reports of casualties or damage in Tartous, a strategic coastal province that hosts a Russian naval facility.

While there has been no official comment on the incident yet, pro-government Sham FM radio reported that Syrian air defence systems were intercepting an Israeli attack over Tartous.