The surprise offensive on Aleppo by Syrian rebel groups has left the US in the difficult position of not fully supporting either side while also maintaining a force posture of nearly 1,000 troops in Syria as part of the ongoing mission to fight ISIS.

In just a few days, a patchwork of rebel forces has seized control of a broad stretch of land in the west and northwest of Syria. But it’s unclear just how much support Syria’s weakened allies can provide.

The Syrian army has upped its airstrikes on Monday against the rebel forces that took Aleppo, with Iran-backed Iraqi militias crossing the border to aid President Bashar al-Assad’s government, according to local reports.