"Explosions resound in Damascus and its countryside as a result of Israeli airstrikes on military sites," the Syrian Observatory for Human Rights war monitor said.

The monitor, which relies on a wide network of sources across Syria, said Syrian air defence forces had been deployed to counter the strikes.

Pro-government media stated Syria had intercepted "enemy" air strikes, usually a reference to Israeli strikes, and Syria's state news agency SANA confirmed that "explosions were heard in the Damascus sky".

Since civil war broke out in Syria in 2011, Israel has carried out hundreds of air strikes against its neighbour, targeting government troops as well as allied Iran-backed forces and Hezbollah fighters.

While Israel rarely comments on individual strikes, it has acknowledged carrying out hundreds of them.

The Israeli military says the strikes are necessary to prevent its arch-foe Iran from gaining a foothold on its doorstep.

Last month Israeli strikes on Damascus International Airport rendered its runways unusable for weeks.

Besides the extensive damage caused to civilian and military runways, the monitor said the strikes had targeted nearby warehouses used as weapons depots by Iran and Hezbollah.

The conflict in Syria started with the brutal repression of peaceful protests and escalated to pull in foreign powers and global jihadists.

The war has killed nearly half a million people and forced around half of the country's pre-war population from their homes.