The early morning strikes hit positions of Iran-backed militias outside the town of Albu Kamal in Deir Ezzor province, killing mostly Pakistani fighters, the Syrian Observatory for Human Rights said.

Syrian state media did not report the attack and Israel rarely acknowledges individual strikes, but the Observatory has accused the Jewish state of launching at least two other aerial attacks against pro-Iran forces in Syria since Saturday.

Early on Wednesday, at least eight Iran-backed fighters were killed in strikes near Damascus and in southern Syria, according to the war monitor, which is based in the UK but relies on a network of sources inside Syria.

On Saturday night, air strikes near Albu Kamal killed at least 14 pro-Iran militia fighters from Iraq and Afghanistan, the Observatory said.

Iran backs President Bashar al-Assad's regime in Syria's civil war.

The latest strikes came after Israel's ambassador to the United Nations Gilad Erdan called on the Security Council to take immediate action to remove Iranian forces from Syria.

"Israel ... demands a total rollback of Iran and its proxies from Syria and the removal of Iranian military infrastructure from Syrian territory," he said in a letter addressed to the head of the UN Security Council.

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

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.