Syrian rebels, led by Islamist groups, have reportedly launched a massive offensive to take over the northern city of Aleppo, a rights watch group said.
The Syrian Observatory for Human Rights said that hundreds of rockets and missiles were fired by rebels into government-held areas in a series of simultaneous attacks on several districts, reported the BBC.
It added that the Syrian troops had responded by returning fire and conducting air strikes.
According to analysts, the fall of Syria's second largest city would mark a major setback for the Assad regime.
The London-based monitoring group said that the fierce clashes killed four civilians, five rebel fighters and injured over 70 others.