DAMASCUS -- An Israeli drone attack targeted and destroyed a weapons depot in the coastal Syrian city of Jableh before daybreak Thursday, the Syrian Observatory for Human Rights reported.

The attack carried out via drones and warplane missiles leveled the depot and caused massive explosions heard from long distances, said the UK-based watchdog group.

It added that the Syrian air defenses and Russian forces responded to the attack within 40 to 50 minutes. The depot is situated near the Hmeimim Air Base, the largest Russian air base in Syria, located in the northwestern province of Latakia.

No immediate reports of casualties have been reported.

While there is no official confirmation, the pro-government Sham FM radio said the sounds heard in the skies over Jableh were the air defenses intercepting targets off the coast.

It added that firefighting teams headed to a site in the vicinity of Jableh after columns of fire were seen rising from it, but no information was provided about its nature.

This latest attack follows a series of Israeli airstrikes in Syria this week.

On Wednesday, two Lebanese nationals, including Hassan Jafar Qasir, the son-in-law of late Hezbollah leader Sayyed Hassan Nasrallah, were killed in an Israeli airstrike on a residence in the Mazzeh Western Villas neighborhood of Damascus.

On Tuesday, an Israeli missile strike hit a site about 500 meters from Wednesday's target, killing three people, including a journalist, and injuring nine others.

Israel frequently conducts airstrikes in Syria, targeting what it says are positions linked to Iran and Hezbollah.