U.S.-backed and Kurdish-led Syrian forces say they have begun the final push to defeat the Islamic State group in the last pocket it holds in eastern Syria.
Bali says the aim of the current push is to end the military presence of "Daesh terrorists." He was using an Arabic acronym to refer to the extremists.
The Kurdish-led SDF launched its offensive to end the IS presence in Syria in September, a battle that left hundreds of fighters dead on both sides.
Syrian opposition activists say Islamic State militants have attacked U.S.-backed fighters near an oil field in the country's east, triggering airstrikes by the U.S.-led coalition.
The Britain-based Syrian Observatory for Human Rights says 12 IS gunmen attacked the Kurdish-led Syrian Democratic Forces and clashed with them for several hours until most of the attackers were killed early Saturday.
Other activist collectives, including the Step news agency, reported the attack, saying some of the attackers used motorcycles rigged with explosives.
The fighting was concentrated near al-Omar field, Syria's largest.
The SDF, backed by U.S. air power, has driven IS from large swaths of territory it once controlled in northern and eastern Syria, confining the extremists to a small pocket of land near the border with Iraq.