File photo: Smoke rises from buildings in the area of Bughayliyah, on the northern outskirts of Deir Ezzor, Syria, Sept. 13, 2017. AFP
The Kurdish-led Syrian Democratic Forces (SDF), who are backed by Washington, said they had "driven out the regime gunmen who had infiltrated the Dheiban area" of Deir Ezzor province in the clashes which erupted on Monday.
Earlier this month, the same area saw 10 days of clashes between the SDF and armed Arab tribesmen in which 90 people were killed.
Britain-based monitor the Syrian Observatory for Human Rights said the latest clashes erupted when pro-government fighters crossed the Euphrates river, which separates pro-government forces in southwestern Deir Ezzor from the SDF in the northeast.
It said 21 of the dead were Damascus loyalists and three were SDF fighters. A woman was also killed.
The SDF said the loyalist fighters had crossed the Euphrates "under cover of an indiscriminate bombardment" of its positions.
The clashes earlier this month erupted after the SDF's arrest of a local Arab military commander who had previously been an ally.
The SDF said at the time that it had driven out the detained commander's supporters among the area's Arab tribes.
It insisted the dispute was an entirely local one and not the result of any wider rift between its Kurdish-dominated forces and the Arab communities which form a majority in some areas under its control.
According to the Observatory, which has a wide network of sources inside Syria, some of the Arab fighters who fled to government-held territory after the clashes earlier this month took part in this week's assault.
The SDF was Washington's main Syrian ally in its fightback against the Islamic State group, which culminated in the jihadists' defeat in their last Syrian foothold on the left bank of the Euphrates in 2019. It continues to enjoy US support.