Iraq's special forces are struggling to clear areas retaken from IS along Mosul's eastern edge, where the militants have built up fortifications and ramparts in residential areas.
The slowdown highlights the challenges ahead for Iraqi forces as they press into more populated areas deeper in the city - where the civilian presence means they will not be able to rely as much on airstrikes.
"There are a lot of civilians and we are trying to protect them," said Lt Col Muhanad al-Timimi. "This is one of the hardest battles that we've faced till now."
Some civilians are fleeing the combat zone, while IS militants are holding others back for use as human shields, making it harder for Iraqi commanders on the ground to get approval for requests for US-led coalition air strikes.
Iraq's special forces are some of the country's best troops, but they still largely rely on air support to clear terrain.
Iraqi forces first entered the eastern edge of the city on Tuesday. On Friday, forces began pushing into Mosul proper, but so far have only advanced just over a mile into the city. On the city's southern front Iraqi forces are still some 12 miles from the city centre.
The extremists captured the city in 2014, and have had plenty of time to erect fortifications. Trenches and berms have turned the streets and alleyways of a district once named after former Iraqi leader Saddam Hussein into a maze, and concrete blast walls have blocked off access to other areas.
"Daesh dug trenches that they filled with water and they have a lot of suicide attackers and car bombs," said Lt Col al-Timimi, using the Arabic acronym for the IS group.
IS fought back on Saturday, pushing the special forces from the southern edge of the Gogjali neighbourhood, where the troops had made their first major foray into the city itself after more than two weeks of fighting in its rural outskirts.
Both sides fired mortar rounds and automatic weapons, while the Iraqi troops also responded with artillery. Snipers exchanged fire rooftops in residential areas.