Syrian state media also reported the blasts at the Mazzeh airbase, on the western outskirts of Damascus, but did not mention any casualties.

The Syrian Observatory for Human Rights war monitor said Mazzeh was hit by a "possible Israeli missile, which hit a munitions store setting off successive explosions".

"It left two pro-regime fighters dead and wounded another 11, some of them in critical condition," said Observatory chief Rami Abdel Rahman.

He could not specify their nationalities or whether they belonged to militias or government forces.

An Israeli military spokeswoman declined to comment on Sunday.

AFP's correspondents in Damascus heard multiple blasts overnight, one of which lit up the sky in a deep red hue, but reported calm on Sunday morning.

A Syrian military source said the Mazzeh airbase "was not the target of Israeli aggression", according to the official SANA news agency.

"The explosions heard were due to an explosion at a munitions deposit close to the airport which was due to an electrical short circuit," the source said, without mentioning any casualties.

The Mazzeh airbase houses Syrian Air Force intelligence, and in early 2017 the Syrian government accused its neighbour Israel of bombing the base.

Israel has sought to avoid direct involvement in the conflict but acknowledges carrying out dozens of air strikes in Syria to stop what it says are deliveries of advanced weaponry to its Lebanese enemy Hezbollah.

It has also pledged to prevent its arch foe Iran from entrenching itself militarily in Syria, and a series of strikes that have killed Iranians in Syria have been attributed to Israel.

Earlier this week, Israel reiterated its threat to hit Iranian military targets in Syria.

"The IDF (Israel Defence Forces) will continue to take strong and determined action against Iran's attempts to station forces and advanced weapons systems in Syria," Prime Minister Benjamin Netanyahu said.

In July, Syria accused Israel of bombing a military post in the northern province of Aleppo, where at least nine pro-regime fighters were killed according to the Observatory.

More than seven years since Syria's conflict began, regime forces have managed to retake entire regions from rebels and jihadists and now control nearly two-thirds of the country.

Syrian troops are supported military by their Russian and Iranian allies, Tehran-backed Hezbollah fighters as well as Iraqi, Iranian and Afghan militiamen.