Syria said Wednesday its counteroffensive has pushed back insurgents attempting to advance to the strategic central city of Hama, while the insurgency says it captured more Syrian troops and Iran-backed militants in fierce battles.

Rebel forces in Syria have seized control of most of the city Aleppo after launching a surprise offensive against government forces, a war monitor reported on Saturday as Russia says it deployed fighter jets against rebels in Syria.

Syrian rebels launched a surprise attack on Saturday and quickly advanced through several provinces in the north and northwest of Syria, including the city of Aleppo, the country’s second largest city.