The raids near Damascus and in Homs province late Sunday killed the fighters, but it was not immediately clear exactly how the civilians died -- whether in the strikes or in the aftermath, the Syrian Observatory for Human Rights said.

It said the strikes hit several Iranian positions near Damascus and targeted a research centre and a military airport west of the city of Homs where the Lebanese Shiite movement Hezbollah and Iranians are deployed.

One of the pro-regime fighters killed was Syrian, while the rest were of other nationalities, Observatory chief Rami Abdel Rahman said.

State news agency SANA earlier said four civilians had been killed after its air defences responded to an Israeli attack.

"Our air defences confronted enemy missiles launched by Israeli warplanes... towards some of our positions in Homs and in the vicinity of Damascus," SANA said, quoting a Syrian military source.

An Israeli military spokeswoman declined to comment on the report.

Israel has carried out hundreds of air strikes in Syria since the beginning of the conflict in 2011, targeting forces loyal to President Bashar al-Assad and the regime's allies Iran and Hezbollah.