BEIRUT: A double suicide car bombing at the Bab al-Hawa border post between Syria and Turkey on Monday killed at least 16 people, including six rebels, a monitoring group said.

The Syrian Observatory for Human Rights, updating an earlier toll, said 20 people were wounded as one car detonated at a checkpoint just outside the crossing and another inside the post.

The border crossing in Idlib province of northwest Syria is held by Islamist and moderate rebels who have been locked in fierce fighting with jihadists from the Islamic State of Iraq and the Levant in recent weeks.

ISIL fighters on Monday took control of the Jarrah military airport in the northern province of Aleppo that had been in rebel hands since February 2013.

Islamist and moderate rebels angered by ISIL's alleged abuses have forced them from Aleppo city but the group has managed to strengthen its grip on the town of Raqa, also in northern Syria.

On Monday, ISIL imposed a Taliban-style ban on music and smoking in Raqa, declaring them un-Islamic.

In a statement it said it would "ban the sale of music CDs, music players, and playing songs in cars and buses and in shops and all places."

The group added it had taken the step because musical instruments and singing are "proscribed in Islam because they distract from remembering God and the Koran".

In a second statement, ISIL said as part of efforts to "apply sharia (Islamic) law... it is completely forbidden to sell cigarettes or water pipes in any place".

Such bans are reminiscent of those the Taliban imposed on television, cinema and music in Afghanistan when in power up until 2001.

ISIL has alienated activists and other opposition fighters in Syria, who accuse it of imposing a reign of terror on areas where it operates.

Its actions provoked a backlash from powerful rebel groups in early January, and the group is now fighting opposition forces in several parts of northern Syria.

The Observatory said Monday that ISIL fighters "withdrew after midnight yesterday (Sunday) from the western Aleppo countryside and evacuated their positions".

The Britain-based Observatory also reported heavy clashes between jihadists and rebels on the outskirts of the town of Azaz in Aleppo province, near the border with Turkey.

Rebel groups in the town shelled areas where ISIL fighters were with mortar rounds, the Observatory said.

Meanwhile regime troops pressed operations across Syria.

The Observatory, which relies on a network of activists and doctors on the ground for its reports, said government air raids on Sunday had killed at least 44 people, including 16 children, across Aleppo province, and in the southern province of Daraa.

Further air raids on Monday killed another five people in Daraa, the Observatory added.