A war monitor on Saturday said three pro-Iran fighters, including at least two Iraqis, were killed in an overnight air strike in eastern Syria near the Iraq border.
According to the Syrian Observatory for Human Rights, the strike occurred in Deir Ezzor province. Iran wields significant influence in the area, which is regularly targeted by Israel and sometimes by the United States.
"Two of the dead were Iraqi nationals with the Islamic Resistance in Iraq and the third was not identified," 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 of jihadists 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 mainly targeting army positions and Iran-backed fighters including from Lebanon's Hezbollah group.
Israel rarely comments on individual strikes in Syria.
In late March, the Observatory said 16 Tehran-affiliated fighters, including an Iranian Revolutionary Guard, 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, but has said repeatedly that it has no combat troops in Syria, only officers to provide military advice and training.