Iranian-backed Iraqi militias have deployed in Syria to back the government's counteroffensive against a surprise advance by insurgents who seized the largest city of Aleppo, a militia official and a war monitor said Monday.

Insurgents led by jihadi group Hayat Tahrir al-Sham launched a two-pronged attack on Aleppo last week and moved into the countryside around Idlib and neighboring Hama province. Government troops built a fortified defensive line in northern Hama in an attempt to stall the insurgents' momentum while jets on Sunday pounded rebel-held lines.