The Syrian military has carried out a series of air strikes after rebel forces launched a major assault to take control of the northern city of Aleppo.
The Syrian Observatory for Human Rights said rebels fired hundreds of rockets and shells into at least seven government-held areas late on Thursday.
By Friday morning, they had made small advances, the monitoring group added.
But the Syrian state news agency Sana said the assault had been repelled and more than 100 "terrorists" killed.
Aleppo, once Syria's commercial and industrial hub, has been divided roughly in half between government-held areas in the west and rebel-controlled eastern quarters for almost three years.
Fighting on the ground and government air strikes have left thousands dead, and destroyed more than 60% of the Old City, a Unesco World Heritage site.