Beirut (AFP) - Syria's army advanced on Friday to the outskirts of a key Islamic State group bastion that is also being targeted by Turkey's army and allied forces, a monitor said.

The Britain-based Syrian Observatory for Human Rights said regime soldiers and allied fighters were now 1.5 kilometres (one mile) from Al-Bab in northern Syria.

The Observatory said the forces had made "important progress" and taken a village near the town, the jihadist group's last major stronghold in the northern province of Aleppo.

Al-Bab is being targeted by both regime forces and an alliance of Turkish troops backed by Syrian rebel forces.

The town has been besieged since Monday, when government forces advancing from the south cut off a road leading into Al-Bab.

Turkish troops and allied forces have been advancing towards the town from the north, east and west.

On Thursday, five Turkish soldiers were killed in the battle for the town, bringing the army's toll to 10 over two days, according to Turkey's state-run Anadolu news agency.

Turkey on August 24 began an unprecedented campaign inside Syria against IS and Kurdish militia which initially made rapid progress but has become mired in a deadly fight for Al-Bab since December.

According to Dogan news agency, 66 Turkish soldiers have now been killed in the Syria operation since it began in August, mostly in attacks by IS.

Turkish Foreign Minister Mevlut Cavusoglu suggested that once Al-Bab was captured Turkey and its allies could send special forces to take Raqa, the jihadists' de facto capital to the southwest.