The multiple explosions hit government-held Tartus and Homs, as well as Hasakeh, which is mostly controlled by Kurdish forces but where the regime maintains a presence.
The assailants detonated two bombs at the entrance of the government stronghold of Tartus along the international coastal highway, which killed 30 persons, SANA news agency said.
A car bomb at the Arzoneh bridge was followed by a suicide bomber wearing an explosive belt who targeted the gathering crowd.
“Two terrorist blasts on Arzuna bridge, the first a car bomb and the second a suicide bomber who detonated his explosive belt when people gathered to help the wounded,” state television said.
Syrian TV aired footage showing massive damage to the area, with a number of smashed cars and the bloodied body of a guard at the checkpoint, where the blast had taken place.
The Britain-based Syrian Observatory for Human Rights monitoring group, which maintains a network of contacts inside the country, put the toll at 47 dead.
There were no immediate claims of responsibility for the blasts, but the Islamic State group has regularly targeted several of the areas hit on Monday.