"They are not even animals; they are worse than animals."

A Kurdish military officer described Islamic State (ISIS) militants this way after revealing the various ingenious ways by which they plant explosive devices to stall the Iraqi Army-led campaign to recapture Mosul, Iraq's second biggest city which fell to ISIS in 2014.

Colonel Nawzad Kamil Hassan, an engineer with the Kurdish forces, said his unit has cleared more than 50 tonnes of explosives from areas once controlled by ISIS, The Guardian reported.

Hassan one of the bombs they found was hidden under a teddy bear that was designed to explode upon taking the cuddly toy—something that a child would find irresistible to do.

"Why would ISIS use something nice, like a bear or a rabbit? They used this toy because they know the peshmerga [Kurdish fighters] will not touch it, but children will," Hassan said.

The Kurdish officer said the homemade explosive devices they found showed the ingenuity, intelligence and resources that ISIS devotes to kill its enemies.

He said ISIS bomb makers have been turning toys, playing cards, abandoned watches, hoses, old clothes, piles of mud and stones, discarded pieces of plywood, and other common objects into detonators to trigger deadly explosions.

In Sinjar city, Hassan said his men cleared five tonnes of explosives from a single school. His engineers check every pile of stones or rubble, every door and window, and every apparently discarded or abandoned object, aware that a single mistake could lead to loss of lives.

"Every day there is a new device. Some of our men have disposed of things that others have not even seen before," he said.

Hassan's men have little protective equipment. As a result, two have been killed and 15 injured while they were trying to clear recaptured areas.

He said the war has become a shadowy battle of wits as they try to find and defuse explosive devices planted weeks, even months, earlier.

Hassan said most of the ISIS bombs are manufactured to lie in wait for their victims. The most common of these bombs are the improvised explosive devices that to an untrained eye may look like just a tangle of wires.

The Kurdish military officer said ISIS will continue to think up new ways of delivering death unless it is deprived of the space and resources.

"They are not even animals," he says, picking up the deactivated teddy bear. "They are worse than animals."