A surprise offensive by rebel forces opposed to Syrian President Bashar al-Assad's regime has led to a new round of fighting in a largely static civil war.

The sudden assault by Syrian rebels has rapidly redrawn the civil war’s front lines and threatened once again the authority of President Bashar al-Assad.

Aleppo, once a symbol of Assad’s triumph in the Syrian Civil War, has again become a battlefield as rebel forces have seized the city.

Rebel groups have launched the largest offensive in years against government forces, capturing the city of Aleppo.

The 13-year civil war in Syria has roared back into prominence with a surprise rebel offensive on Aleppo, one of Syria's largest cities and an ancient business hub. The push is among the rebels' strongest in years in a war whose destabilizing effects have rippled far beyond the country's borders.

Forces opposed to President Bashar al-Assad have captured the Aleppo airport and are attacking the western city of Hama, according to local officials and a Britain-based war monitor.

The surprise rebel offensive that has seized Aleppo and threatens other regime-held territories could mark a further weakening of Iran's regional sway but also spur a new cycle of violence and

Syrian opposition fighters have made their most significant advance in years against government forces, shaking up a civil war that had long been at a stalemate. The new rebel offensive began on Wednesday in Aleppo Province in northwestern Syria.