Turkey's state-run news agency says three Turkish soldiers have been killed in Syria in the battle to retake the northern town of al-Bab from the Islamic State group.

The Anadolu Agency, citing unnamed military sources, says 11 Turkish soldiers were also wounded in the fighting on Wednesday, including one who was reported to be in critical condition.

The report says intense clashes are underway near a hospital in the town that the militants were using as a shelter and to store arms and ammunition.

Turkey sent ground troops into northern Syria in August to support Turkey-backed Syrian opposition forces in clearing a border area of Islamic State group militants and to curb Kurdish territorial expansion.

At least 24 Turkish soldiers have been killed so far in the operation, entitled Euphrates Shield.