The UN has said Islamic State had killed 40 former members of the Iraqi security forces on Saturday
Iraqi special forces have fought their way into Mosul for the first time in more than two years, entering an outer neighbourhood following a fierce battle.
They made their way into Gogjali after using tanks, artillery and machine gun fire to attack Islamic State jihadists who used guided anti-tank missiles in retaliation.
Airstrikes from coalition jets helped the attack despite IS lighting fires to try to obscure the aerial view with smoke.
Major General Sami al Aridi said that by noon special forces had "stormed in" and were just 800 metres from the more central Karama district.
Concrete blast walls have been set up to slow their advance and bombs laid on the road, he added.
The fight for the city could now become much more drawn out, with house-to-house battles and fighters embedded among a civilian population, potentially lasting months.
The vital first steps into Mosul came as the UN said Islamic State had killed 40 former members of the Iraqi security forces on Saturday, throwing their bodies into the River Tigris.
It also tried to move some 25,000 people - most probably to use as human shields.
UN human rights spokeswoman Ravina Shamdasani said trucks and minibuses had transported them from a town south of Mosul called Hammam al Alil in the early hours of Monday.
Most minibuses turned back under pressure from fighter jet patrols, she said, but some did reach Abusaif, 9 miles (15km) north of Hammam al Alil.
In the nearby village of Bazwaya, recaptured two days ago, white flags hung from buildings on Tuesday - put up by residents to show they would not resist the liberation.
Children made V for victory signs, but hundreds of families now face life in a displaced persons camp.
Iraqi forces - made up of the army, Kurdish forces and various militia - began the massive push to retake Mosul two weeks ago.
It is the country's second biggest city and Islamic State's last major stronghold in Iraq.
With a US-led coalition providing air support, progress has so far been quicker than some expected and dozens of villages and several towns around Mosul have been captured.
Iraqi forces plan to besiege the city and open safe corridors for the million-plus civilians still believed to be living there.
With fears of a potential humanitarian crisis, aid agencies are also poised to provide emergency shelter and food and water.