The Britain-based watchdog added that four others were killed by Syrian government airstrikes on the towns of Kafarya and Kafr Nabl in Idlib and on a town in the province of Hama.
The observatory said the number of deaths is likely to increase as there are wounded civilians, some of them in critical condition.
Since late April, the forces of Syrian President Bashar al-Assad, supported by Russian air power, started a massive campaign against rebels in the provinces of Hama and Idlib, the last major opposition stronghold in the country.
The offensive has so far killed 641 civilians and displaced more than 300,000 people, according to the observatory.
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The observatory said the number of deaths is likely to increase as there are wounded civilians, some of them in critical condition.
Since late April, the forces of Syrian President Bashar al-Assad, supported by Russian air power, started a massive campaign against rebels in the provinces of Hama and Idlib, the last major opposition stronghold in the country.
The offensive has so far killed 641 civilians and displaced more than 300,000 people, according to the observatory.
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