Thousands of Syrian insurgents have pushed on with their advances on government-held areas in the country’s northwest.

Insurgents have breached Syria's second-largest city, Aleppo, clashing with government forces, according to a Syria war monitor and fighters.

The advance on Aleppo followed a shock offensive launched by insurgents Wednesday, as thousands of fighters swept through villages and towns in Syria’s northwestern countryside. Residents fled neighborhoods on the city’s edge because of missiles and ...