A massive truck bomb claimed by rebels killed at least 35 people in a government-controlled village in the central Syrian province of Hama.
More than 50 people were injured in the attack in Al-Horra.
The attack has been blamed on rebels fighting to overthrow President Bashar al-Assad.
A policeman said: "It is estimated that the explosives weighed three tonnes."
The Islamic Front, a rebel coalition, claimed responsibility.
It said on Twitter that a radio-controlled bomb had targeted a "gathering of Assad militia".
The Syrian Observatory for Human Rights said 38 people were killed.
It claimed that civilians as well as security personnel, and more than 40 injured.
Elsewhere, a suicide bomber killed one person and injured at least 20 at a security checkpoint in Lebanon's Eastern Bekaa Valley.
The attack took place on the main route joining Lebanon and Syria's capitals, Lebanese police said.
The Lebanese checkpoint is situated in an area where Lebanese Sunni Muslim militants opposed to President Assad have been carrying out attacks on areas under the control of the pro-Assad Shia Hezbollah movement.