Israeli strikes on several areas of Syria overnight killed at least 23 fighters, including five Syrian regime troops and 18 other allied forces, a monitor said Thursday.

The Britain-based Syrian Observatory for Human Rights said an officer was among the regime troops killed in the strikes and that the casualties included foreigners.

Israel's army said it hit dozens of Iranian military targets in Syria.

The Russian defence ministry, whose country has forces in Syria supporting the regime, said 28 Israeli warplanes took part in the raids and around 70 missiles were fired.

Areas near Damascus and in the southwest of Syria were among the targets, the Observatory said.

The strikes "caused human losses in a number of the targeted areas", it said, adding the death toll was likely to rise.

Israel said it targeted Syrian positions after rocket fire towards its forces in the Israeli-occupied Golan Heights that it blamed on Iran.

A senior military pro-regime source in Syria confirmed the salvo of rockets but insisted Israel fired first.

The strikes come after the Syrian army late Tuesday said it intercepted two Israeli missiles, while the Observatory said eight Iranians were among 15 foreign pro-regime fighters killed in that attack.

Since the start of Syria's civil war in 2011, Israel has repeatedly targeted positions of the Syrian army and Lebanon's Shiite movement Hezbollah backing it inside the country.