Troops are pushing into the last Islamic State stronghold in the country's second largest city.
Iraqi forces say they have launched an assault on Mosul's Old City, the last district held by Islamic State.
Lieutenant General Abdul-Amir Rasheed Yar Allah, who commands army operations in Ninevah province, says Iraqi special forces, the regular army and police are taking part in the operation to retake Mosul's Old City, which began on Sunday.
The IS group captured Mosul when it swept across northern and central Iraq in the summer of 2014. Iraq launched a massive operation to retake the city last October.
Up to 150,000 civilians are believed to be trapped in the Old City, where the militants are using them as human shields, UN humanitarian co-ordinator Lise Grande told The Associated Press on Friday.
She said conditions are "desperate," with little food and no clean water.