Iraqi officers say troops are advancing cautiously into eastern districts of Mosul where they face stiff resistance from Islamic State militants.

Airstrikes, automatic fire and artillery were heard from dawn and one soldier was reported killed in clashes. Civilians, some of them wounded, could be seen fleeing the fighting.

The officers say Iraqi forces are aiming to take complete control of the city's Tahrir area and from there move into the adjacent Muharabeen district.

They spoke on condition of anonymity because they weren't authorized to talk to the media.

Iraqi forces launched the long-awaited operation to retake Mosul a month ago but have only advanced into a few eastern districts. The troops have faced fierce resistance, with snipers, mortar fire and suicide bombers driving armor-plated vehicles packed with explosives.