The strike occurred in Deir Ezzor province, where Iran wields significant influence and which is regularly targeted by Israel and the United States, according to the Syrian Observatory for Human Rights.

"An Iraqi member in the Islamic Resistance in Iraq was killed, and two others were injured in a preliminary toll, as a result of an unknown airstrike," the Observatory said, referring to a loose alliance of Iran-backed groups.

The Britain-based monitor, which relies on a network of sources inside Syria, said an explosion was heard coinciding with the strike "in Albukamal countryside... a few kilometres away from Syrian-Iraqi borders".

Iraq's Sayyed al-Shuhada Brigades announced the death of a fighter in a strike on "Friday which targeted his vehicle during a reconnaissance patrol on the Iraqi-Syrian border", accusing the United States of being behind the attack.

Responsibility for the strike was not immediately claimed, but a spokesperson for the US-led military coalition formed in 2014 to fight the Islamic State group told AFP that "neither the coalition nor US forces carried out overnight strikes in Deir Ezzor".

The Observatory said that several hours before the strike, drones flew over the area.

Since the beginning of the Syrian civil war in 2011, Israel has carried out hundreds of strikes primarily targeting pro-Iran groups -- which it rarely comments on publically.

In late March, 16 Tehran-affiliated fighters, including an Iranian military advisor, were killed in strikes on eastern Syria.

The strikes also killed one civilian working for the World Health Organisation.

Iran has long been a key ally of the Syrian government, most notably providing military advisors.

burs-jos/dcp