AS ISLAMIC State leaders and fighters flee the battle for Mosul, a network of booby-trapped tunnels reveals the extremist group is increasingly living like rabbits underground.

The battle for Mosul has revealed a network of abandoned tunnels and cramped living quarters outside the city, showing the extremist group is increasingly forced to operate, and live, underground amid a punishing air campaign and mounting territorial losses.

In the village of Badana, east of Mosul, two years of IS rule resulted in a network of tunnels, fully stocked, but now abandoned.

When IS fighters moved into the territory around Mosul more than two years ago, the group attacked with convoys that traversed the open desert and held parades in the city centre.

Now, they seek refuge, mount their attacks from underground, and leave booby traps in their wake.

Badana was taken back from IS control on the second day of attacks designed to take Mosul, Iraq’s second-largest city, and it offers a glimpse of the battle still in store.

Above the ground, AP reports, walls are shredded by air strikes and artillery fire, homes are black with soot from the resulting fires, and anything standing has been looted.

Underneath, in the tunnels, bags of fresh vegetables — even eggs beside a makeshift stove — lie abandoned, suggesting IS fighters maintained their supply lines until just days before their defeat, and their hasty exit.

Amid sleeping bags and food, there were even reports of the discovery of a booby-trapped Koran.

In other villages, deep tunnels booby trapped with explosives run under houses, and antipersonnel device mines lie half-buried in roads.

“They spent their lives in these tunnels,” said Tahseen Muhammed Sharif, a Kurdish fighter who said the forces that drove the militants out of the village also found ammunition inside the tunnel network.

“I can’t imagine living like this,” he said.

“There is a definite difference between us and them — their behaviour, it’s outside human behaviour.”

A small unit of Iraqi Kurdish fighters tasked with holding the territory in and around Badana, were camped on Tuesday in a field behind a row of armoured vehicles on the village’s edge. While free of IS fighters, the area is littered with dozens of booby-trapped explosives. Kurdish fighters stick to paths and roads they have already used and walk in single file.

As residents return to check the devastation, they are shocked by what greets them.

War experts warn it will only get worse as the advance on Mosul continues.

When Iraqi forces reach the city, Patrick Martin of the Institute for the Study of War in Washington DC said they should expect to see defences like the tunnel networks and booby-trapped explosives of Badana, but on a much greater scale.

“They’re making sure that whenever the operation to retake the city commences it will be extremely difficult for the security forces to do so,” Mr Martin said, adding that while there were reports of IS fighters fleeing Mosul, the group had shown a willingness to defend the city by using car bombs, suicide bombers and trenches.

Faced with punishing air strikes by the US-led coalition, the IS fighters have changed tactics.

They melt into civilian populations and building tunnels, so they could move without being seen from above.

During the first day of the operation, the most complex for Iraq’s military since the withdrawal of US troops in 2011, Kurdish forces say they retook nine villages and pushed the front line back 8km.

Like Badana, those villages were almost empty of civilians, allowing coalition aircraft to largely clear the territory from the air.

Kurdish Lieutenant Colonel Fariq Hama Faraj said he and his men have received orders they will not advance any further in the Mosul fight.

But he does not believe this will be the last time he fights IS.

“They will come back with a new name and they’ll be more extreme and more barbaric,” he said.

“If you look to the history of these organisations we see that each one is more extreme than the last.”

After a string of victories in the past year, Iraqi ground forces have pushed IS out of more than half the territory the group once held in Iraq, with close support from the US-led coalition. Now, with the launch of the campaign to retake Mosul, the extremists’ main stronghold, Iraqi forces are again operating under coalition air cover.

An estimated 3500 to 5000 IS fighters are dug into Mosul, while tens of thousands of Iraqi forces have massed to recapture Iraqi’s second city.