Twenty-one people were wounded, the Observatory added.
On April 30, the Syrian government, supported by Russian air power, began a massive military offensive against rebels in the provinces of Hama and Idlib, forcing thousands of people to flee.
Syrian government forces have since regained territory from the rebels in the two provinces.
According to the Observatory, some 4,941 people have lost their lives, among them 1,274 civilians, since the offensive started.
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