The Britain-based Syrian Observatory for Human Rights said a total of 271,138 people have lost their lives in the war which broke out on March 2011.
The dead include 79,106 civilians, of whom 13,500 children and 8,760 women.
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Non-jihadist rebel fighters killed in the conflict numbered 46,452, while Islamists and extremist fighters -- including foreigners -- numbered 44,254.
The Observatory said the death toll also includes 97,842 pro-regime fighters, over half of them government troops.
The new toll marked an increase of over 10,000 deaths since the monitoring group gave its last count in December.
On Monday, the US and Russia announced a ceasefire deal that would see an end to fighting between forces loyal to President Bashar al-Assad and rebel groups from Saturday.