Under Mosul's Fifth Bridge, which crosses the Tigris just north of the old city, tanks and armoured vehicles are lined up in reserve.

Angry shouting alerts the men resting on their machines to a throng of soldiers storming past - a man, stripped down to a pair of baggy trousers and his hands tied, is being pushed along. One soldier holds him by the hair, as another kicks him from behind. The captive pleads for mercy as soldiers crowd around him.

Eventually, he is led up the road to a makeshift detention centre, set up to screen those fleeing Mosul's old city.

The old city, where pockets of fighting continues, was the final holdout for Islamic State of Iraq and the Levant (Isil) fighters and their families as they mounted a last stand before the city was declared liberated last week.

Wives of some of the fighters launched suicide attacks as Iraqi forces approached. Iraqi soldiers have come to consider anyone still trapped inside the Old City as the enemy.

Fleeing Iraqi civilians walk past the heavily damaged al-Nuri mosque credit: (AP Photo/Felipe Dana)

"All of the men in there are with Daesh, and most of the families are Daesh families," said Sergeant Fazel, a soldier of the Iraqi 9th Armoured Division, using the Arabic acronym for Isil.

As a result, soldiers' treatment of civilians has become rougher, and little help is afforded to the emaciated women, children and the elderly struggling to make their way to safety in the blazing heat.

Any man of fighting age is suspected to be a jihadist trying to escape, with mounting reports of swift executions behind the front lines, as rights group warn that adherence to the laws of war have “collapsed”.

The fate of the man led away from Mosul's Fifth Bridge is unknown.

But The Telegraph witnessed another man, bushy-bearded and haggard, being detained by soldiers, believed to be Iraqi counter-terrorism troops, last week near the ruins of the notorious al-Nouri mosque.

His shirt and jeans hung awkwardly from his lean frame and his hands were tied behind his back with a strip of cloth. His head bowed, he walked along without protest, before the soldiers pushed him into a shop in a bombed-out house.

Shots rang out, and the soldiers emerged to walk back to their position at the frontline. Inside the building, the man lay dead on a bed of rubble, a bullet wound in his forehead, his hands still tied together.

Human Rights Watch says there have been “numerous” eyewitness accounts of torture and extrajudicial killings.

The nine-month fight to defeat the Islamic State group in Mosul ended in a crescendo of devastation credit: AP Photo/Felipe Dana

A recent video filmed in the area appeared to show a group of soldiers severely beating a detainee before throwing him from a cliff onto the riverbank and shooting him. The corpse of another man already lay there. It is not the first time Iraqi forces have been accused of carrying out atrocities in the battle to liberate the Isil stronghold.

In May, Iraqi photographer Ali Arkady risked his life to document the widespread torturing and killing of Isil suspects by an elite Iraqi unit.

But observers say the targeted violence has become more brazen as the battle for Mosul draws to a close.

"Numerous witnesses on the frontline have been giving me detailed reports of not only a significant increase in the torture and extrajudicial killing of Isil suspects being captured as they flee the old city, but a change in tenor, with armed forces no longer feeling that they need to hide these actions from the eyes of international observers," said Belkis Wille, senior Iraq researcher at Human Rights Watch.

Among the troops, "a collapse of adherences to the laws of war" has set in, she said.

Colonel Saad, the spokesman for the 9th Division, described the accusations as "fabrications". "We treat prisoners according to the law," he said.