BAGHDAD/MOSUL, Iraq (Reuters) - Iraqi troops who briefly seized a Mosul hospital believed to be used as an Islamic State base were forced to withdraw from the site, but managed to establish a base for army tanks nearby after days of fierce back-and-forth fighting, residents said.

Iraqi forces backed by tribal militias during battle to retake a village from the Islamic State on the eastern bank of the river Tigris, Iraq December 7, 2016. REUTERS/Mohammed Salem

The rapid advance into the Wahda neighborhood where the hospital is located marked a change of tactic after a month of fighting in east Mosul in which the army has sought to capture and clear neighborhoods block by block.

The ferocity of the fighting reflects the importance of the army’s push from southeast Mosul towards the center, their deepest advance in a grueling seven-week offensive to crush Islamic State in Iraq’s largest northern city.

The soldiers seized Salam hospital, less than a mile (just over 1 km) from the Tigris river running through central Mosul, on Tuesday but pulled back the next day after they were attacked by six suicide car bombs and “heavy enemy fire”, according to a statement by the U.S.-led coalition supporting Iraqi forces.

Coalition warplanes, at Iraq’s request, also struck a building inside the hospital complex from which the militants were firing machine guns and rocket-propelled grenades, it said.

The soldiers involved in the action are at the spearhead of a U.S.-backed, 100,000-strong coalition of Iraqi forces including the army, federal police, Kurdish peshmerga fighters and mainly Shi’ite Popular Mobilization forces battling to crush Islamic State in Mosul.

In another part of Mosul already recaptured by government troops, Iraqi police fired shots in the air and threatened to whip crowds with a hose as residents tried to overrun the first distribution of aid by UN agencies inside the city.

The distribution aimed to reach 45,000 people in total at several locations. As word of the aid spread, residents of the Zuhour neighborhood flocked to a boys’ primary school chosen as a distribution point.

Hundreds surged forward against just a handful of men pushing to close the gate. They burst through, and began climbing over the walls and pushing in through the exit until the police, firing shots in the air and wielding long sticks, managed to regain control.

Saad Salih, 56, came in an electric wheelchair, pushed by a neighbor because there was no electricity in Mosul to charge it. “We need everything,” Salih said.

“GATES OF HELL”

Defeating the militants in their Iraq stronghold would mark a major step in rolling back the caliphate declared by the jihadists in parts of Syria and Iraq when they took over Mosul in mid-2014.

But with two years to prepare themselves, retreating fighters have waged a lethal defense, deploying hundreds of suicide car bombers, mortar barrages and snipers against the advancing soldiers and exploiting a network of tunnels to ambush them in residential areas.

Soldiers from the army’s Ninth Armored division were left exposed on Tuesday after punching into the Wahda neighborhood.

“When we advanced first into Wahda, Daesh (Islamic State) showed little resistance and we thought they had fled,” an officer briefed on the operation told Reuters by telephone. “But once we took over the hospital, the gates of hell opened wide.”

“They started to appear and attack from every corner, every street and every house near the hospital,” said the officer, who declined to be identified because he was not authorized to speak to the media. He said insurgents may also have used a tunnel network reaching into the hospital complex itself.

A nurse at the hospital said that when the Iraqi army approached on Tuesday, Islamic State guards removed the militants being treated there, including some field commanders. Staff and civilian patients took shelter in the basement as fighting erupted around the hospital half an hour later.

A resident who lives just 300 meters away, a veteran of Iraq’s eight-year war with Iran in the 1980s, said he had never seen such fierce fighting.

“It was very violent warfare - they used all sorts of weapons, it’s not traditional war. There were explosives, suicide attackers, mortar barrages and planes, everything,” he told Reuters by telephone.

After three days of fighting, Iraqi tanks and armored vehicles had managed to assemble at a site in the Wahda neighborhood, a resident said.

“LIKE GHOSTS”

The statement by the coalition said Iraqi troops “fought off several counter-attacks and six VBIEDs (car bombs) ... before retrograding a short distance, under heavy enemy fire”.

The Iraqi officer said that when the troops were inside the hospital complex, fighting off the militants, they came under attack from suicide bombers who he said either infiltrated through tunnels or had been hiding in the hospital grounds.

“We don’t know, they were like ghosts,” he said.

Iraq does not give casualty figures or report on its equipment losses, but the officer said 20 soldiers were killed and around 20 armored vehicles were destroyed or damaged.

Those figures could not be confirmed. Islamic State’s Amaq news agency said more than 20 military vehicles were destroyed and dozens of soldiers killed. It showed a picture of a smoldering tank, its turret blown off, next to a crater.

Around 280 km (175 miles) southwest of Mosul dozens of people, mainly civilians, were killed on Wednesday in air strikes which hit a western Iraqi town close to the border with Syria, local parliamentarians and hospital sources said.

They said the strikes hit a busy market area in the Islamic State-held town of Qaim, in the overwhelmingly Sunni Muslim province of Anbar. Among the victims were 12 women and 19 children.

An Iraqi military statement said Iraqi air force planes conducted air strikes “on a terrorist hideout” in the area shortly after noon on Wednesday, as well as a second attack on an unspecified location.

It said at least 50 terrorists were targeted in the air strikes. It gave no details of civilian casualties, but said that the region - and all information coming out of it - was controlled by Islamic State.