As a walkie-talkie carried word of another casualty from an Islamic State mortar attack, an Iraqi policeman peered through leaves at enemy positions just across the Tigris River. He kept his head low to avoid snipers but also had an eye on the sky.

Minutes later, the militants sent a drone overhead. It carried out surveillance and dropped an explosive. Then mortar bombs landed nearby, sending the policemen running for safer ground.

More than three months into the battle to drive them from their biggest stronghold, the hardline Sunni militants of Islamic State remain lethal and determined, despite being driven from the eastern half of the city of more than a million people.

Few are more acutely aware of the danger they pose than police Lt-Colonel Falah Hammad Hindi, who instructed his men to take cover as mortars landed ever closer.

"The weapon of choice is the drone," said Hindi, whose unit faces sometimes 16 drone attacks in a single day as well as mortar bombs and snipers.

Read more:  Reuters