An elite Iraqi army unit advanced towards the built-up area of the Islamic State stronghold of Mosul on Monday after two weeks of fighting to clear surrounding areas of the insurgents.

Military commanders said that the U.S.-backed offensive to recapture Mosul -- the largest military operation in Iraq since the U.S.-led invasion that toppled Saddam Hussein in 2003 -- could still take weeks and possibly months.

"The battle of Mosul will not be a picnic," Hadi al-Amiri, leader of the Badr Organisation, the largest Shi'ite militia fighting with Iraqi government forces, said from the southern frontline.

"We are prepared for the battle of Mosul even if it lasts for months".

Troops from the Counter Terrorism Service (CTS) were moving in on Gogjali, an industrial zone on Mosul's eastern outskirts, and could enter it later on Monday, an officer from the U.S.-trained unit told a Reuters correspondent just east of Mosul.

The zone lies about a kilometer from the administrative border of Mosul.

More at Reuters.