The missile attack on Monday night hit weapons depots and military positions belonging to Syrian regime forces and Iran-backed militia fighters south of Damascus, according to the Syrian Observatory for Human Rights.

The attack wounded at least seven Syrian troops, according to the official SANA news agency, which said the missiles were launched by warplanes over the Israeli-occupied Golan Heights.

The five killed were all non-Syrian paramilitary fighters, according to the Observatory.

It added that 11 combatants were wounded in total -- four non-Syrian fighters and seven Syrian troops, of which two were in critical condition.

A military spokesman in Israel told AFP that its army "does not comment on foreign reports".

Israel has launched hundreds of strikes in Syria since the start of the country's civil war in 2011.

It has targeted government troops, allied Iranian forces and fighters from the Lebanese Shiite militant group Hezbollah, saying its goal is to end Tehran's military presence in Syria.

It rarely confirms details of its operations in Syria but says Iran's presence in support of the regime is a threat and that Israel will keep up strikes.

The nine-year-old conflict in Syria has killed more than 380,000 people and displaced more than half of the country's pre-war population.