Opposition activists said amateur video footage, posted on a website, showed the moment a bomb hit the crowd. Another video showed the aftermath - grey smoke filling the air before clearing to show bodies.
The body of the man who activists said was killed a day before lay wrapped in a white shroud on the ground. Moments earlier it was being held above the head of mourners as they marched down the street.
The footage showed the bodies of those activists said had been killed in the explosion, some barely recognisable and others with limbs missing. The pro-opposition Syrian Observatory for Human Rights said the death toll was likely to rise due to the number injured.
The Syrian authorities severely restrict the media, making it extremely difficult to verify such reports. Activists film attacks by government forces who have been trying for 16 months to crush an uprising against President Bashar al-Assad.
The United Nations has said more than 10,000 people have been killed by Assad's forces, while Syria has said at least 2,600 members of the military and security forces have been killed by what it calls foreign-backed "Islamist terrorists."