The area had been reinforced with concrete barriers and snipers
Iraqi special forces fighting so-called Islamic State (IS) fighters have broken through the frontline without suffering losses, a spokesperson has said.
Sabah al-Numan told the BBC that many IS fighters had been killed.
Government forces entered the city's outskirts for the first time on Tuesday since the city was seized in June 2014. IS fighters were strongly resisting the siege, reinforcing the area with concrete barriers, sniper sand suicide bomb squads.
It was being reported that the Golden Division, the first brigade of Iraqi forces, took heavy casualties as they tried to press forwards into the district of Gogjali, on the edge of the city.
Mr al-Numan, a spokesman for the Counter Terrorism Service (CTS) said: "We broke the front line of the centre of Mosul. We liberated a very important area which is the main gate for Mosul from the east.
"We had a very tough fight with ISIS in this area and we could liberate it very fast and also without any casualties, in front of many dead and executed from ISIS."
Mosul is last major urban stronghold of IS in the country.
Today marks the 17th day of the anti-IS operation, which involves 50,000 personnel including Kurdish fighters.
Elite troops seized control of the state TV building in Kukjali on Tuesday hours after launching an assault on the eastern district and later breached the outskirts of the Karama district.
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.
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.