MOSUL, Iraq — Iraqi forces have won a string of swift territorial gains in Mosul in the fight against the Islamic State after months of slow progress. Government troops retook the eastern edge of a third bridge in Mosul on Saturday and a cluster of buildings inside Mosul university, according to a senior Iraqi officer overseeing the operation.

Islamic State fighters overran Mosul in the summer of 2014, announcing from there their self-styled ‘‘caliphate’’ after taking a large swath of Iraq and Syria in a lightning surge. Access to the city’s central bank, a large taxable civilian population, and nearby oilfields quickly made the Islamic State the world’s wealthiest terrorist group.

Yet even as a punishing campaign of US-led coalition airstrikes has pushed the militants underground, Islamic State leaders continued to use Mosul as a key logistical hub for planning meetings. If recaptured by the Iraqi forces, Islamic State territory in Iraq that once stretched across a third of the country would be reduced to small pockets in the north and west that troops will likely be able to mop up relatively quickly.

Iraqi forces now control the eastern sides of three of the city’s five bridges that span the Tigris river connecting Mosul’s east to west. Warplanes from the US-led coalition bombed the city’s bridges late last year in an effort to isolate Islamic State fighters in the city’s east by disrupting resupply routes.

At Mosul University, senior commanders said that Iraqi forces have secured more than half of the campus Saturday amid stiff resistance, but clashes were ongoing into the afternoon. Iraqi forces entered the university from the southeast Friday morning and by nightfall had secured a handful of buildings, Iraqi army officers said on a tour of the university Saturday.

Thick clouds of black smoke rose from the middle of the sprawling complex Saturday morning. By afternoon, clashes had intensified with volleys of sniper and mortar fire targeting the advancing Iraqi forces. Convoys of Iraqi Humvees snaked through the campus, pausing for artillery and airstrikes to clear snipers perched within classrooms, dormitories, and behind the trees that line the campus streets.

As Iraqi forces have closed in on the Tigris river that roughly divides Mosul into eastern and western halves, their pace has quickened. Islamic State defenses in the city’s east appear to be thinning and unlike in the surrounding neighborhoods, Iraqi officers said they believe Mosul university and recently retaken government buildings are largely empty of civilians — allowing them to use air power more liberally. Medics in a small field hospital in eastern Mosul said civilian casualties have dropped significantly.

Iraqi soldiers at Mosul university said while they were still coming under heavy small arms fire, Islamic State resistance was significantly less than they faced during the first weeks of the Mosul operation.

‘‘We were targeted with only four car bombs where before [the Islamic State] would send 20 in one day,’’ special forces Lieutenant Zain al-Abadeen said. ‘‘And they aren’t armored like before, they’re just using civilian cars.’’