Syria's air defence system has been activated against an "Israeli aggression" in Damascus, state news agency Sana said late Tuesday.

Israeli planes arrived from Lebanese air space, reported Sana, which said there had been "explosions in Damascus".

The news agency gave no indication of any deaths or damage.

The Syrian Observatory for Human Rights, a Britain-based war monitor, said Israeli air strikes in central Syria killed at least 11 army troops and militiamen late Tuesday."At least seven army soldiers and four National Defence Forces militiamen were killed,"

Observatory chief Rami Abdul Rahman told AFP, adding that all of the dead were Syrian.

The observatory said the strikes targeted air force positions near the village of Khirbet al-Tin on the outskirts of Homs, as well as an arms depot belonging to the Lebanese Hizbollah movement.

The air strikes targeted an area "close to Damascus's international airport, as well as a Syrian air force battalion in the Dumayr region", around 50 kilometres from Damascus, where "explosions took place at arms depots", according to the observatory.

"Air strikes also took place in the south of Homs province" while "explosions were felt in the provinces of Hama and Latakia" in the north and northwest respectively.

"The strikes have led to human losses in Homs, where rescue teams have been despatched to the targeted sites," the observatory said, without giving a toll.

Since the start of the war in neighbouring Syria in 2011, Israel has carried out hundreds of air strikes on Syrian territory, allegedly targeting army positions as well as allied Iranian forces and members of Lebanon's Hizbollah movement.

Israel regularly reiterates that it will not allow Syria to become a stronghold of its sworn enemy Iran.