Israeli air strikes on Syria have killed four pro-Iranian fighters allied to the Damascus regime, a Britain-based war monitor said on Friday.

Syrian state media earlier said its air defence system engaged "hostile targets" over the capital Damascus late on Thursday.

"The Israeli enemy launched an aerial attack... targeting positions near Damascus and around the city of Homs," a military source told state news agency SANA.

"Our air defence responded to the missiles and shot most of them down."

The Syrian Observatory for Human Rights said the Israeli missiles had targeted "arms depots and military positions” belonging to Lebanese Shiite movement Hizbollah, in the Qarah area in the northwest of Damascus province, near Homs province and the Lebanese border.

The strikes had killed four members of the Iran-backed group, but it was not immediately clear whether they were Syrian or Lebanese, the Britain-based war monitor said.

Lebanese media also earlier reported two missiles had fallen in the Qalamoun region.

The Israeli forces rarely acknowledges its strikes in Syria and a spokesperson told AFP it did "not comment on foreign media information”.

However, since the start of the war in Syria ten years ago, Israel has carried out hundreds of air strikes on Syrian territory, targeting regime positions as well as allied Iranian forces and members of Hizbollah.

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

The Syrian conflict, which began in 2011 with the regime’s repression of pro-democracy protests, has grown increasingly complex over the past decade, drawing in more and more parties.

According to the observatory, the war has left nearly half-a-million people dead