Eight Syrian fighters working with Iran's Revolutionary Guards were killed on Tuesday in a knife attack on their position in eastern Syria's Deir Ezzor province, a war monitor said.
The Syrian Observatory for Human Rights said "unidentified armed individuals" raided the position in the Syrian desert, in the second deadly attack on pro-Iran fighters in two days in the Mayadeen area.
The eight dead fighters "worked under the command" of Iran's Guards and were "slaughtered" using knives, said Rami Abdel Rahman, head of the Britain-based Observatory, which relies on a network of sources in Syria.
Control of Deir Ezzor is split between US-backed Kurdish-led forces to the east of the Euphrates river and Iran-backed Syrian government forces and their proxies to the west, while Islamic State (IS) group jihadists are also active in the province.
On Monday the Observatory said gunmen killed three Syrians who were also working with the Revolutionary Guards, in an attack on a military position on the outskirts of Mayadeen city.
Iran-backed groups have bolstered regime President Bashar al-Assad's forces since the start of Syria's civil war in 2011.
Thousands of pro-Iran proxy fighters are deployed in Deir Ezzor province, according to the Observatory.
While IS was defeated territorially in Syria in 2019, its remnants continue to carry out deadly attacks particularly in the vast Badia desert which runs from the outskirts of Damascus to the Iraqi border.
The border area is a key segment of the route that pro-Iran armed groups use to move fighters, weapons and even consumer goods between Iraq and Syria.