Troops reported to have captured a bridge leading to the old city while aid agencies struggle to accommodate displaced people

Nearly three weeks into the last phase of the battle for Mosul, Iraqi forces have started pushing into the most heavily fortified and lethal corners of the crumbling city.

This weekend the battles in the city, the Islamic State’s last urban stronghold in Iraq, were some of the most intensive yet. Maj Gen Haider al-Maturi, of the federal police commandos division, said Isis militants had dispatched at least six suicide car bombs, which were all destroyed before reaching troops. He said the militants were moving from house to house and deploying snipers.

A statement released by Iraqi Rapid response teams said units were “very close” to the government buildings near the old city. It added that units had captured the Danadan district, south-east of the complex, while US-trained counter-terrorism service units pushed through the Tal al-Ruman and Somood districts, in the south-west.



Early on Monday, US-backed Iraqi forces captured the city’s al-Hurriya bridge, which leads to the old city centre from the south, a military media officer told Reuters.



Facebook Twitter Pinterest Men fleeing Isis-controlled areas were asked to remove their shirts to prove they were not wearing suicide vests. Photograph: Goran Tomasevic/Reuters

As the fighting has intensified, so too has the displacement of west Mosul residents, with more than 45,000 fleeing in the past week – a higher number than expected.



The pace has accelerated in recent days as the fighting approached the most densely populated parts of west Mosul, and aid agencies have expressed concern that camps to accommodate people fleeing the city are almost full.



The International Organisation for Migration’s Mosul displacement tracking matrix showed the number of people uprooted since the start of the offensive in October exceeded 206,000 on Sunday, up from 164,000 a week earlier.



The number may still rise sharply. Up to 650,000 civilians are thought to remain in the city, and their exodus would strain resources, especially as a short spring turns into a long, hot desert summer.

Civilians who fled on Sunday ran the gauntlet of snipers and explosions in the ruins of neighbourhoods on the edge of the government zone, where Iraqi forces are pressing their offensive. Men and boys were forced to remove their shirts as they ran from Isis territory towards Iraqi military positions.

Ahead of the troops is a labyrinth of tunnels and fortifications prepared over the past two years. Above that area is the Nouri mosque, a key emblem of the terror group’s control of Mosul, where the Isis leader, Abu Bakr al-Baghdadi, made his one and only public appearance in mid-2014 to proclaim himself caliph. Intelligence agencies believe the area around the mosque has remained important to senior Isis leaders.



Before the push to retake the city, Baghdadi was an occasional visitor to the mosque, an intelligence chief told the Guardian earlier this year. Since then he has remained to the north-west of the city, moving in a band between the Iraqi villages of al-Ba’aj and Billij, the border town of Bukamal and the Syrian town of Shedada.



Much of the senior Isis leadership is believed to have abandoned Mosul, leaving its defence to up to 5,000 battle-hardened ideologues, who have laid multiple ambush points, house bombs and booby-traps in the narrow roads and lanes, which are impassable to armoured vehicles.

Also playing out as expected is the unrestrained savagery of the extremist group’s fightback, which has included widespread use of human shields and suicide bombers and, according to medics, the use of chemical weapons.



The International Committee for the Red Cross (ICRC) said a chemical attack by Isis last week killed several people and maimed at least seven more. Residents in the already cleared east Mosul neighbourhood where the attack took place said at least five rockets or mortars struck the area at around 3pm on 26 February. One witness spoke of a strong odour and said several victims had severe burns.



A woman was taken to Rozhawa hospital in Erbil with severe blistering. She told medics that a rocket had hit her house in an area that had been declared safe in early February.

Isis used chemical weapons earlier in the war, firing shells containing chlorine and other chemicals at Kurdish troops to the north of the city. It has also been accused by the Organisation for the Prevention of Chemical Weapons of using mustard gas against a rebel community in northern Syria early last year.

That attack caused symptoms similar to those experienced by victims in the latest strike. However, there has been no determination yet of what agent was used. “This is horrible,” said the UN humanitarian coordinator in Iraq, Lise Grande. “If the alleged use of chemical weapons is confirmed, this is a serious violation of international humanitarian law and a war crime.”

Even with the foothold established by Iraqi forces, recapturing the rest of the city is unlikely to happen in the next two months, according to an Iraqi general. “We are well prepared for this,” he said. “But so are they. This is our most difficult fight. It will be hard to win it without a lot of damage and casualties.

“There was a road to the west that we expected to see them flee to. Some have and have been rounded up. But not as many as we thought. The rest want to stay and die.”

The operation to retake Mosul officially began in October after more than two years of slowly clawing back territory from Isis militants. The terror group overran nearly a third of Iraq – including Mosul, the country’s second largest city – in the summer of 2014.