The Turkish army and its allies on Saturday entered the Islamic State (IS) militant group's bastion of Al-Bab in northern Syria, the Syrian Observatory for Human Rights monitoring group said.
"They entered Al-Bab from the northwest after violent clashes with the jihadists as Turkish artillery bombarded the town," the Observatory's Rami Abdel Rahman said.
Heavy fighting was ongoing late Saturday in the town near the Turkish border, he said, which has been under IS control since 2014.
Al-Bab is the last bastion IS has in northern Aleppo province.
In August, Turkish troops entered northern Syria in an unprecedented operation Ankara said targeted both IS and Kurdish fighters.
Turkish media said on Friday it was sending 300 commandos to reinforce its military campaign inside Syria.
The offensive comes as a US-backed Arab-Kurdish alliance presses an offensive on IS's de facto Syrian capital of Raqa southeast of Al-Bab.