The strikes on Saturday night in Deir Ezzor province, on the border with Iraq, were likely carried out by Israeli war planes, the Observatory said.

The Israeli army said it doesn't comment on foreign reports.

More than 10 strikes hit positions of Iran-backed militias outside the border town of Albu Kamal, according to the war monitor.

The attack killed eight Iraqis and six Afghan fighters, it said.

It also destroyed two bases as well as several military vehicles, the Observatory added.

Iran-backed fighters are heavily deployed in a stretch of territory between the Syrian towns of Albu Kamal and Mayadeen, both former strongholds of the Islamic State group.

Along with Russia, Iran has been a key backer of the Damascus regime in its nine-year-long civil war.

Israel has carried out hundreds of air and missile strikes on Syria since the civil war broke out in 2011, targeting Iranian and Lebanese Hezbollah forces as well as government troops.

The Israeli army rarely acknowledges individual strikes.

Syria's war has killed more than 380,000 people and displaced millions more since starting in 2011 with the brutal repression of anti-government protests.