In the northern city of Aleppo, explosives stashed in a kiosk blew up, killing one person, the group said, while rebels in the south killed two soldiers at a checkpoint.
Government forces stormed the southern town of Dael, raiding activist homes and setting some on fire, the Observatory said. Another group, the Local Coordination Committees, said more than 20 homes had been damaged.
Residents could not be reached for comment and activists' claims could not be independently verified. The Syrian government rarely comments on specific incidents and bars most media from working inside the country.
Syria's uprising began in March 2011 as part of the Arab Spring with peaceful protests calling for political reforms. Assad's regime sent tanks, snipers and thugs to try to quash the revolt, and many in the opposition have taken up arms to defend themselves and attack government troops.
Albert Aji in Damascus and Vladimir Isachenkov in Moscow contributed to this report.
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