By Maya Gebeily BEIRUT (Reuters) -Syrian rebels opposed to President Bashar al-Assad said on Friday they had reached the heart of the northern city of Aleppo, after a surprise sweep through government-held towns and nearly a decade after having been forced out of the city.

Rebel forces in Syria have taken control of several neighbourhoods in the country's second-largest city, Aleppo, according to the UK-based monitoring group Syrian Observatory for Human Rights (SOHR).

A rebel commander said a fall in Iran-backed manpower created an opening this week's assault. Iran's ally Hezbollah has suffered big losses to Israel.

Insurgents breached Syria’s largest city Friday and clashed with government forces for the first time since 2016, according to a war monitor and fighters, in a surprise attack that sent residents fleeing and added fresh uncertainty to a region reeling from multiple wars.

Syrian armed rebels have entered Aleppo just three days into their surprise offensive, marking the first time they have set foot in the country’s second largest city since government forces recaptured the city in 2016.

Rebel forces in Syria say they have entered Syria's second-largest city, Aleppo, in the biggest offensive against the government in years. Video posted on a channel affiliated with the rebels appears to show their fighters in vehicles inside the city.