The seizure of the Iron Bridge, linking eastern Mosul with the terrorist-held Old City on the west side, means the government holds three of the five bridges over the Tigris and bolsters Prime Minister Haider al-Abadi's assertion that the battle is reaching its final stages, Reuters reported.
The bridge, which was damaged in fighting late last year, was captured by federal police and Interior Ministry Rapid Response units, a police statement said.
The gains were made in heavy fighting in which troops fought street-by-street against an enemy using suicide car bombs, mortar and sniper fire, and grenade-dropping drones to defend what was once their main stronghold.
"Our troops are making a steady advance ... and we are now less than 800 meters from the mosque," a federal police spokesman said.
Losing the city would be a huge blow to Daesh as it has served as the terrorist group's de facto capital since its leader Abu Bakr al-Baghdadi proclaimed himself head of a caliphate spanning Iraq and Syria from the Nuri Mosque in July 2014.
The capture of the mosque would thus be a huge symbolic victory as well as a concrete gain. But many hard days of fighting could still lie ahead as government forces try to make headway in the streets and narrow alleyways of the Old City.
Daesh terrorists have booby-trapped houses, and government forces will also be fighting amongst civilians, ruling out the extensive use of air and artillery support.
Heavy fighting was also reported on Wednesday around the Mosul museum by journalists and combatants. A Daesh suicide car bomb exploded near the museum. Helicopters strafed the ground with machinegun fire and missiles.
The intense combat marked a decisive stage in the battle for Mosul which started on Oct. 17 last year, and in the wider struggle against Daesh.
As well as waging terror in Iraq and Syria, the terrorists have inspired attacks in cities in Europe, Africa and elsewhere that have killed hundreds of civilians.
In Baghdad, Abadi said: "Daesh become day after day surrounded inside a tight area and they are in their final days."
In a news conference on Tuesday night, he warned the terrorists that they must surrender or face death.
Residents have streamed out of western neighborhoods recaptured by the government, many desperately hungry and traumatized by living under the terrorist group's harsh rule.
As many as 600,000 civilians are still trapped with the terrorists inside Mosul. The Ministry of Immigration and Displacement said on Tuesday that in recent days almost 13,000 displaced people from western Mosul had been given assistance and temporary accommodation each day, adding to the 200,000 already displaced.