(Updates death toll)
BEIRUT, Jan 20 (Reuters) - Two car bombs hit a rebel-held post on the Syrian border with Turkey on Monday, killing at least 16 people and closing the frontier, opposition activists and fighters said.
The Bab al-Hawa crossing is held by a rebel alliance called the Islamic Front, which has been fighting with the Islamic State in Iraq and the Levant (ISIL), a small but powerful affiliate of al Qaeda with a core of foreign fighters.
It was not immediately clear who had planted the bombs. The attack occurred a few days after a car bomb that killed 26 in the eastern city of Jarablus and which activists blamed on ISIL.
More than 1,000 rebels have died in clashes between rival groups in the last three weeks in an upsurge of internecine violence that has weakened the nearly 3-year-old armed campaign to topple President Bashar al-Assad.
The anti-Assad Syrian Observatory for Human Rights, a Britain-based monitoring group, said at least six of the dead from Monday's bombing were Islamist fighters. It said the rest were likely civilians, and that about 20 others were wounded in the blasts.
Syrian rebels in Bab al-Hawa, in the northwestern province of Idlib, said the border was shut on the Turkish side. A Syrian activist at Bab al-Hawa said the two car bombs exploded within 10 minutes of each other.
The governor's office in neighbouring Turkish Hatay province said the explosion was on the Syrian side of the border. Its press spokesman Cahit Dogan said there were no reports of damage or injuries on the Turkish side. (Reporting by Oliver Holmes and Stephen Kalin in Beirut and Ayla Jean Yackley in Istanbul; Editing by Robin Pomeroy)