Video footage posted online claims to show the aftermath, with people carrying away the wounded and a wide area reduced to rubble.
Activists say families are buried under the rubble in one neighbourhood.
Meanwhile, opposition politicians say they have agreed to form a government for rebel-held areas.
Umbrella group the Syrian National Coalition, meeting in Cairo, said it would meet again in Istanbul on 2 March to name a prime minister.
The UN estimates that about 70,000 people have died since the uprising against President Bashar al-Assad's regime began in March 2011.
Voice of Russia, BBC