More than 300 people were also wounded in the Monday attacks in the Mediterranean coastal cities of Jableh and Tartus, some of them critically, the Syrian Observatory for Human Rights said.
Islamic State number two killed in US raid in Syria
Most of the dead were civilians, among them eight children.
The two cities, which are majority Alawite -- the offshoot of Shia Islam followed by Assad -- had been relatively insulated from Syria's five-year civil war.
Trail of death: String of bombings kill 189 in Syria, Yemen
IS claimed the blasts in a statement, saying they were in retaliation for air strikes by the regime and its Russian ally and threatening "more devastating and bitter attacks".
The Syrian foreign ministry blamed "the regimes of hate and extremism" in Qatar, Saudi Arabia and Turkey, the leading supporters of rebels fighting to overthrow the regime.
Delicate Syria truce takes effect
More than 270,000 people have been killed since the conflict erupted in 2011. Millions more have been driven from their homes.
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