A suicide bomber driving a truck packed with 1.5 tonnes of explosives killed at least 30 people and wounded dozens in Syria's central city of Hama.
State media reported the man blew himself up inside the vehicle on a busy road on the outskirts of the city.
It blamed the attack on "terrorists", the term it uses to describe rebel forces trying to topple President Basharal-Assad.
The pro-opposition Syrian Observatory for Human Rights said the attack targeted an army checkpoint.
Syria's two-and-a-half-year-old conflict began as peaceful protests but has degenerated into civil war.
Rebels have been joined by hardline Islamists, some of them linked to al-Qaeda, and several groups have used suicide bombs to attack military and political targets.
Pictures on Syria TV showed firemen trying to put out huge fires and black clouds of smoke rising from charred trucks and cars.