Iraqi forces have retaken around two thirds of the eastern half of Mosul from the Islamic State group since the start of an offensive in mid-October, a top commander said Sunday.

"From east Mosul... more than 60 percent" has been retaken from IS, Staff Lieutenant General Abdulwahab al-Saadi, a top commander in Iraq's Counter-Terrorism Service (CTS), told AFP.

He was speaking from his headquarters northeast of Mosul, where IS proclaimed a "caliphate" in June 2014 after seizing the city.

Iraq's elite CTS forces are the best-equipped, best-trained and most seasoned forces in the country but the going has been tough since Prime Minister Haider al-Abadi announced the beginning of an operation to retake Mosul on October 17 last year.

Hundreds of thousands of civilians remain inside Iraq's second city, forcing Iraqi and allied forces to take precautions and slowing their advance.

CTS and other forces more recently deployed inside the city have been moving house-to-house, dodging sniper fire, suicide car bombs and booby traps to retake one neighbourhood after another.