Hassan, who held a rank equivalent to major general, was killed Saturday by one of his aides who worked with the Grandchildren of Prophet Brigade, which is affiliated with the Free Syria Army, the sources told the pan-Arab network.
Hassan's death occurred amid reports of yet another massacre in Daraya, a town near Damascus.
Early Sunday, nine more bodies were discovered in Daraya. The Local Coordination Committees of Syria told CNN about 25 people were killed across the country.
On Saturday, CNN said a total of 440 people were killed in the highest single-day death told to date, more than 200 in Daraya. An official of the Local Coordinating Committees told CNN it was unclear when the people were killed in Daraya, as it has been under attack for about six days.
The BBC said about 200 bodies were discovered in houses and basement shelters Saturday in Daraya. Abu Kinan, an activist in Daraya, told Sky News most of the victims had been shot by troops conducting house-to-house raids. "In the last hour, 122 bodies were discovered and it appears that two dozen died from sniper fire and the rest were summarily executed by gunshots at close range," Sky News quoted him as saying
The official Syrian news agency SANA said Sunday the country's "armed forces continue to pursue terrorists in Aleppo and disinfect Daraya and eliminate a number of them and confiscate their weapons."