The Syrian government has accused Turkey, Qatar and Saudi Arabia of being behind a wave of bombings in the coastal cities of Tartous and Jableh.
The state-run news agency Sana said the attacks constituted a "serious escalation", and were aimed at derailing peace efforts.
State media said at least 78 people were killed, while a monitoring group put the death toll at more than 145.
So-called Islamic State (IS) has said it was behind the attacks.
The cities, on Syria's Mediterranean coast, are part of the heartland of President Bashar al-Assad and have, until now, escaped the worst of the civil war.
Sana said letters condemning the bombings had been sent from the foreign ministry to the UN.
"The ministry asserted that these terrorist bombings constitute a serious escalation by the extremist and malicious regimes of Riyadh, Ankara, and Doha," the report said.
"They also seek to derail the Geneva [peace] talks and the cessation of hostilities and truce arrangements, as well as turning attention away from the Syrian Arab Army's achievements in the war against terrorism."
Turkey, Qatar and Saudi Arabia support various rebel forces in Syria but are part of an international coalition battling IS.