Syrian rebels advancing against government forces pushed close on Tuesday to the major city of Hama, rebels and a war monitor said, after their sudden capture of Aleppo last week rocked President Bashar al-Assad.

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.