A massive car bomb killed dozens of people on the Syrian side of the Bab al-Salama border crossing with Turkey on Thursday, a monitoring group and online activists said.
Gruesome photographs posted online by witnesses showed shocked men standing over charred, blackened bodies, some missing limbs.
A video of the scene posted on YouTube showed smoke rising from the tangled remains of a blown-up car and luggage lying abandoned amid the chaos.
The Britain-based Syrian Observatory for Human Rights said 29 were killed in the blast, including women and children.
Online activists put the death toll at much higher.
Al-Akhbar could not independently verify the casualty figure.
The area around the crossing has been targeted by car bombs before.
In February, a blast on the Syrian side reportedly killed six people and wounded 45.
The Syrian side of the crossing is under the control of Islamist rebels who have been battling more radical jihadists from the Islamic State of Iraq and Syria since early January.
Other border crossings between Turkey and Syria have also been targeted, including the Bab al-Hawa post in the northwest, where two suicide bombers killed 16 people in January.