Syrian activists say an explosive-laden vehicle has detonated near a northwestern field hospital.
It was not immediately clear how many people were killed or wounded in the incident.
Activists say the attack happened Sunday in Atmeh, near the Turkish border. Atmeh is in territory held by rebels fighting to overthrow President Bashar al-Assad.
No one has claimed responsibility for the attack.
Meanwhile, activists say a Syrian rebel commander who fought alongside al-Qaida founder Osama bin Laden and was close to its current chief, Ayman al-Zawahiri, was killed by a suicide attack on Sunday
The London-based Observatory for Human Rights in Syria said Abu Khaled al-Soury, also known as Abu Omair al-Shamy, a commander of the Salafi group Ahrar al-Sham was killed along with six comrades by al-Qaida splinter group the Islamic State of Iraq and the Levant (ISIL).
Some information for this report was provided by AP and Reuters.