BAGHDAD, March 30 (Xinhua) -- UN Secretary-General Antonio Guterres arrived here Thursday on an official visit to hold talks with Iraqi officials, an Iraqi foreign minister official told Xinhua.

Guterres is expected to meet with the Iraqi top officials including Prime Minister Haider al-Abadi and President Fuad Masoum to discuss the war against terrorism and the humanitarian situation of hundreds of thousands of displaced people from the war zones in and around Mosul, the official said on condition of anonymity.

The UN chief's visit came as the Iraqi security forces are fighting to dislodge the extremist Islamic State (IS) militants from their last major stronghold in Mosul.

The troops have been fighting street by street and house by house to recapture the Mosul's old city center, but they were slowed by the heavy resistance of IS militants and the presence of some 500,000 people living in the old houses with narrow alleys.

The fierce battles in the western side of Mosul caused heavy casualties among civilians who were either caught by cross-fire or by airstrikes and shelling.

Mosul, 400 km north of the Iraqi capital of Baghdad, has been under IS control since June 2014, when government forces abandoned their posts and fled, enabling IS militants to take control of parts of Iraq's northern and western regions.