Winning a race with pro-Assad forces, Iran, and Russia, the Kurdish-led Syrian Democratic Forces have captured Syria’s largest oilfield.

The US-backed SDF said on Sunday that it completed the takeover of the al-Omar oilfield from the retreating Islamic State in Deir ez-Zor Province in eastern Syria.

Spokesperson Laila al-Abdullah said a “large-scale military operation” took the area “with little damage”, as ISIS fighters holed up in an adjacent housing complex. The assault followed a rapid 60-mile advance, reaching the destination before the Assad regime’s military and its allies could do so.

Al-Omar is located on the east bank of the Euphrates River in eastern Deir ez-Zor near the Iraq border. Pro-Assad forces, enabled by Russia and including Iranian-supported foreign militias, had advanced to the west bank and crossed the river as they hoped to reach the oilfield before the SDF. They are reportedly a few kilometers away, raising the possibility of clashes.

The oilfield is about 10 km (6.2 miles) north of the town of al-Mayadin, seized by pro-Assad forces from the Islamic State in mid-October.

The US-led coalition tried to dampen any thought of a confrontation, saying the sudden, surprise SDF advance and assault was designed to prevent sabotage of oil facilities by ISIS.

The Syrian State news agency SANA has not mentioned the development. However, the pro-Assad propaganda site Al-Masdar sought to minimize the setback by comparing it to the Iraqi Kurdish loss of oilfields near Kirkuk to the central Iraq Government and its forces: “Even with Syria’s Al-Omar oil fields, Kurdish forces lose 150 times more oil in Iraq”.

The Islamic State’s last major position is the town of al-Bukamal, on the Iraq border and across the highway between Baghdad and Damascus. Coaliton spokesman Colonel Ryan Dillon said Sunday, “[The SDF] have made this very quick sprint down to al-Omar, and they have to reinforce that area. The offensive operations on Bukamal will be difficult and will take a lot of forces.”