Turkish troops and Syria rebels enter Islamic State-held town

Turkish troops and Syrian rebels on Saturday entered the Islamic State-held town of al-Bab in northern Syria, as government forces also approached the extremist bastion, a monitor said.

"Turkish forces and allied rebels in the Euphrates Shield campaign entered the western edge of the town and took control of a number of areas," the Britain-based Syrian Observatory for Human Rights said.

The monitor said heavy clashes were underway with IS in the town, which is the group's last stronghold in the northern province of Aleppo.

The town has been seen as a key prize and Syrian government troops and allied forces have also been advancing towards it in a bid to wrest it from IS.

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

By Friday, government forces were just 1.5 kilometres (less then a mile) from the southern outskirts of al-Bab, while Turkish troops and allied rebels advanced from the north, east and west.

Turkey began an unprecedented campaign inside Syria on August 24, targeting both IS and Kurdish militia.

After initial rapid progress, the campaign became mired in the deadly fight for al-Bab since December.

Turkey's Dogan news agency says 66 Turkish soldiers have been killed in the campaign since it started, mostly in IS attacks.

Al-Bab has been under IS control since 2014, when the group seized large swathes of territory in Syria and neighbouring Iraq, proclaiming its self-described caliphate.