Iraqi special forces drove back Islamic State militants in the Mosul University campus on Saturday, while elite police units took over large areas along the east bank of the Tigris river, military officials said.

The head of Iraq's Counter Terrorism Service (CTS) said security forces were close to seizing the entire east bank of the Tigris, which bisects Mosul north to south. That gain will bring at least half of Islamic State's last major stronghold in Iraq back under government control.

Iraqi forces have made rapid advances since the new year, as part of a nearly three-month, U.S.-backed offensive.

For the ultra-hardline Islamic State, losing Mosul would probably spell the end of the Iraqi side of its self-styled caliphate, which it declared in 2014.

The military will be able to begin attacks on western Mosul, which Islamic State still fully controls, once it has captured the eastern bank of the river. The militants have fought back fiercely with car bombs and snipers, and have used civilians as cover.

An air raid during the week targeting a senior IS militant killed up to 30 people, residents said late on Friday.

Islamic State has also carried out attacks in Baghdad where a string of explosions in the last two weeks has killed dozens of people.

Another blast hit central Baghdad late on Saturday, killing at least one person, police sources said. There was no immediate claim of responsibility.

Earlier on Saturday, CTS forces battled IS fighters at the university in Mosul, in a second day of clashes there.

"We entered the university and cleared the technical institute, dentistry and antiquities departments," Lieutenant General Abdelwahab al-Saadi of the CTS told a Reuters reporter in the complex.

"In the coming hours it will be liberated completely," he said.

CTS troops had gathered in the university canteen. As they unfurled a map of the area, a suspected Islamic State drone flew overhead and they shot at it.

The Iraqi forces also found chemical substances IS had used to try to make weapons, CTS commander Sami al-Aridhi said.

The United Nations says the militants seized nuclear materials used for scientific research from the university when they overran Mosul and vast areas of northern Iraq and eastern Syria in 2014.

IS has used chemical agents including mustard gas in a number of attacks in Iraq and Syria, U.S. officials, rights groups and residents say.

POLICE RETAKE SOUTHEAST RIVERBANK

Seizing the university would be a crucial strategic gain and allow Iraqi forces to advance more quickly towards the Tigris in the city's northeast, military officials have said.

Parallel advances in the southeast of the city on Saturday, led by elite rapid response units, put Iraq's federal police in control of large areas along the river bank, a spokesman said.

"The Yarimja area ... has been liberated, a large number of Daesh (Islamic State) elements were killed, and the rest fled to the right-hand side (western bank)," Lieutenant Colonel Abdel Amir al-Mohammedawi told Reuters.

Forces had stopped suicide car bomb attacks by firing at them during their advance, and the federal police also captured a field hospital the militants had been using, he said.

The federal police forces were backed by the Iraqi army's 9th armoured division and by U.S. coalition air support, Mohammedawi said.

A separate military statement said the federal police in the area also captured a highway linking Mosul to the city of Kirkuk to the southeast.

Improved coordination between different military branches, plus new tactics and better defences against the car bombs has helped them gain new momentum against Islamic State in Mosul since the turn of the year, U.S. and Iraqi military officials say.

Lieutenant General Talib Shaghati told state television the entire eastern bank of the Tigris would soon be under Iraqi control.

AIR RAID KILLS CIVILIANS

Advances had slowed in late November and December as troops became bogged down in tough urban warfare after entering the city itself, and Islamic State fought from densely-populated residential areas.

An air raid targeting a senior Islamic State militant on Thursday killed up to 30 people in a western Mosul district, residents said. It was not immediately clear if the strike was carried out by Iraqi forces or the U.S.-led coalition.

Iraq Body Count (IBC), a group run by academics and peace activists that has been counting violent deaths in the country since 2003, said 21 to 25 civilians had died that day in a strike on that area.

Reuters could not independently verify the reports.

Iraqi forces have tried to avoid causing civilian casualties while Islamic State has deliberately shelled and shot at residents.

The United Nations said recently the number of casualties being rushed to hospitals in nearby cities had increased.