As Syrian cities come under artillery and aerial attacks on multiple fronts, Sheikh explained that the FSA, the main armed opposition fighter group in Syria, is becoming more powerful and gaining ground.

“The regime’s army can only attack with warplanes and tanks, but it is now very difficult for ground forces or police patrols to walk around inside the cities with the exception of Damascus,” he said to Al Arabiya.

Sheikh stressed the unity of the Free Syrian Army (FSA) saying the FSA brigades might have different names, but they all belong to one entity.

The institutionalization of the FSA is made possible by the defection of more senior officers in the state army and there have been efforts from other foreign countries he added, criticizing Iran and Russia for backing Assad’s regime

U.S. Secretary of State Hillary Rodham Clinton on Sunday acknowledged deep differences with Russia over how to handle the crisis in Syria, saying she would continue to try to convince Moscow to back increased international pressure on Syrian President Bashar Assad at a news conference at the end of the annual Asia Pacific Economic Cooperation forum summit.

Troops meanwhile bombarded rebels in the key city of Aleppo, as a bomb attack on a bus carrying civilians and soldiers in the province of Homs reportedly killed four people and wounded dozens, according to activists.

The violence followed a bloody day in which as many as 172 people have been killed by the fire of Syrian forces across the country on Saturday, including 89 in Aleppo, according to the Local Coordination Committees.