Fierce clashes raged overnight on the edges of Syria's second city Aleppo after a major rebel offensive, an AFP correspondent said Wednesday.
A coalition of opposition groups fighting under the name "Fatah Halab" - or Aleppo Conquest - launched the assault on President Bashar al-Assad's forces with a tunnel bomb on Tuesday.
Rebel fighters initially advanced from the western suburbs of the city into government-held districts but were pushed back by Wednesday morning, the Syrian Observatory for Human Rights said.
Observatory head Rami Abdel Rahman said the fighting was "the most violent in Aleppo in over a year."