Devastated buildings, piles of rubble and putrid corpses of jihadists: apocalyptic scenes unfold in the Old City of Mosul where Iraqi forces are battling the last Islamic State group fighters.

Lieutenant Colonel Mohammed al-Tamim walks past the body of a jihadist half buried under the ruins of a building in Faruq district, three times within minutes, without giving it a glance.

The body, which has been decomposing for days in scorching heat of 40 degrees Celsius (104 Fahrenheit), is bloated and turning black and the remains let off a pungent smell.

The bearded fighter died holding his weapon.

Lieutenant Colonel Salam al-Obeidi told AFP that he believes only "a few hundred Daesh fighters", an Arabic acronym for Islamic State group jihadists, are left in the Old City.

Three years after overrunning Mosul and making it the de facto Iraqi capital of the "caliphate" they proclaimed, the jihadists now only control about a square kilometre in the city, commanders said.

A warren of alleyways, the Old City resonates with the sound of gunfire from automatic rifles, exploding rockets and the thuds of mortar rounds as Iraqi forces battle the jihadists for their last holdouts.

"Daesh members don't turn themselves in," said Tamim.

"And if they don’t get killed, their last option is to blow themselves up and commit suicide."

Carcasses of motorcycles and scooters that had been rigged with explosives and blown up are scattered along the sides of the Old City's alleyways.

IS fighters have tried repeatedly to slow down the advance of Iraqi forces with suicide attacks.

Rubble from what used to be roofs or facades damaged in the fierce fighting litters the narrow streets, sometimes piled several metres (feet) high.

A soldier who took part in the battle to retake Faruq says air strikes were an important factor because armoured vehicles were unable to be squeezed into the alleyways.

"We advance and determine where enemies are, then we call for air strikes to eliminate them, (and) then we advance, cautiously," said a soldier who did not wish to be identified.

"We see lots of dead bodies. We're searching for the others" who are still alive, he said of the IS fighters.

- Civilians in the crossfire -

The devastation is overwhelming.

Buildings have been levelled entirely, with electrical cables dangling from them and debris from blown up cars found on the upper floors of those still standing.

Once a residential neighbourhood, Faruq has been reduced to a wasteland of flattened buildings and streets filled with chunks of concrete and dust.

Inside the houses that have withstood the fighting, anarchy reigns.

Household items, furniture, clothes and cooking utensils are strewn everywhere, alongside bikes, toys and blankets, but not a soul to be seen.

The Iraqi army says it is taking every possible precaution to avoid harming civilians as it presses its offensive against the jihadists.

Tens of thousands of people are believed to be still trapped in the Old City, half of them children.

The civilians "are our priority and we have helped them," said Lieutenant-General Abdulwahab al-Saadi, from the elite Counter-Terrorism Service (CTS) that has spearheaded the assault.

Iraqi forces launched an assault on the Old City on June 18, eight months into an offensive to retake Mosul, the country's biggest military operation in years.

Hundreds of IS fighters have been killed since the operation started on October 17, hundreds of civilians have also died. More than 800,000 people have had to flee their homes and many are still housed in overcrowded camps.

Survivors of the battle of Mosul say most families have lost one or several relatives, some killed by jihadists, and others due to the fighting.

Civilians who have fled the battleground city say entire families who had sought refuge in the basements of homes occupied by jihadists were killed in the bombardment.

Source: AFP