The operation to drive Isil fighters from Mosul is proceeding ahead of schedule, according to Iraqi and US authorities, as fighting continued in the city's eastern suburbs on Thursday.

Members of Iraq's elite counter terrorism forces reported they were advancing towards the centre of Mosul after breaching the eastern outskirts of the city for the first time since it was overrun by fighters from the Islamic State of iraq and the Levant in 2014 on Tuesday.

The US Special Presidential Envoy for the Global Coalition to Counter ISIL Brett McGurk hailed Iraqi forces entering the eastern suburbs of Mosul as a milestone, writing on Twitter on Thursday: “Ways to go, but ahead of schedule.”

“The plan of the join command in Nineveh is going faster than we planned,” Iraq's Interior Ministry spokesman Brigadier Saad Maan told local news outlet Rudaw in a televised interview. Protecting civilian lives and infrastructure were priorities that could slow their advance, he said.