At least 43 people were killed and more than 80 others were injured when a car bomb went off at a northern Syrian border post on the frontier with Turkey, the Syrian Observatory for Human Rights said.
The explosion on Thursday occurred at a garage near the Bab al-Salameh border crossing in the northern Syrian province of Aleppo.
The garage is used by passengers who come to, or leave the crossing point, said Rami Abdurrahman, the Observatory's chief.
Pictures sent by activists showed burnt cars, charred corpses and body parts in the area.
"At least 12 ambulances have transported wounded people into Turkey, the death toll is very high," an activist in the area told Reuters news agency.
The Local Coordination Committees, another activist group, told Associated Press that a car bomb at the border crossing killed and wounded "many" people.
Such explosions have occurred in the past in border areas near Turkey.
Turkey's private Dogan news agency reported the blast wounded "tens of people" in the Karaj Sajou area. It gave no further details.
Syria's conflict began with largely peaceful protests calling for reforms, transformed into an armed uprising and eventually a civil war following a ferocious military crackdown on protesters.
More than 150,000 people have died since March 2011, while millions have been displaced.
Explosions around Syria have killed and wounded thousands of people during the past three years.