The incident underscores the potential for further conflict in Syria's oil-rich east, where the U.S.-backed Syrian Democratic Forces (SDF) alliance of Kurdish and Arab militias holds swathes of land after its offensive against Islamic State. Last night the U.S. military announced that it had "self defended" against an attack by Syrian government troops on Syrian ground:

More than 100 fighters aligned with Syrian President Bashar al-Assad were killed overnight when U.S. coalition and coalition-backed local forces repelled their attack in eastern Syria, a U.S. official said on Thursday. They "were likely seeking to seize oilfields in Khusham that had been a major source of revenue for Daesh from 2014 to 2017," the official said, using the Arabic acronym for ISIS. The official said that about “20 to 30 artillery and tank rounds landed within 500 metres” of the headquarters before the US-backed fighters and coalition forces “targeted the aggressors with a combination of air and artillery strikes”.”We estimate more than 100 Syrian pro-regime forces were killed while engaging (Syrian Democratic Forces) and Coalition forces. Additionally, Syrian pro-regime forces maneuvered T-55 and T-72 main battle tanks with supporting mortar fire in what appears to be a coordinated attack on Syrian Democratic Forces approximately 8 kilometers (5 miles) east of the Euphrates River de-confliction line in Khusham, Syria," Veale said. In Beirut, an official with Hezbollah said the group has no presence in the area hit by the coalition, adding that those who came under fire were pro-Assad forces known as the Popular Committees, as well as the Syrian National Defense Forces. BEIRUT (AP) — Syrian state-run media said Thursday a rare U.S. strike on government-backed troops in eastern Syria killed and wounded dozens of tribal fighters, calling it a new effort "to support terrorism." "We estimate more than 100 Syrian pro-regime forces were killed while engaging SDF and coalition forces," while one SDF member was wounded, a US military official said. The US military official said the coalition had informed Russia of the presence of pro-regime forces in the area before the attack via a hotline established as part of the de-confliction line, adding that the coalition had observed a buildup of pro-regime troops over the past week. Syrian news agency SANA disputed the US account and said that the US-led coalition had "attacked popular forces that were fighting" armed groups such as Islamic State of Iraq and the Levant (ISIL, also known as ISIS).
United States Central Command says that it killed more than 100 pro-government troops in "self-defense" strikes 8 kilometres (5.0 mi) east of the Euphrates de-confliction line that was reportedly agreed with Russia.