
These devastating pictures show the aftermath of a suicide bulldozer packed with explosives that ripped apart an Iraqi forces advance in the fight for Mosul, leaving four dead.

The bulldozer smashed through vehicles and barricades near the Mosul museum before detonating a blast that destroyed vehicles including an Iraqi US-made Abrahams tank.

A spokesman for the rapid reaction forces said: 'A bulldozer packed with a large amount of explosives managed to reach our troops near the museum using the Old City side roads, we lost an Abrahams tank, three Humvees and four soldiers.'

An ISIS bulldozer exploded near the Old Bridge facing the Old City in Mosul, killing four Iraqi soldiers on Wednesday

An Islamic State suicide car bomb exploded near the Mosul museum on Wednesday, leaving four soldiers dead

Losing the city would be a huge blow to ISIS as it has served as the group's de facto capital since its leader Abu Bakr al-Baghdadi proclaimed himself head of a caliphate spanning Iraq and Syria from the Grand Mosque in the summer of 2014

Iraqi forces battling ISIS in Mosul edged into the Old City and around the al Nuri mosque on Friday trying to seal off a main road to prevent militants sending in suicide bombers to attack their positions

On Wednesday, a suicide bomber in an armoured digger truck penetrated Iraqi forces lines, smashing through vehicles and barricades before detonating a blast that destroyed vehicles

Iraqi army and security forces have made significant gains in recent days in the battle that started in October, seizing a main bridge over the Tigris river and advancing towards the mosque

Iraqi forces battling ISIS in Mosul have advanced into the city's ancient central district as they try to seal off a main road to prevent militants sending in more suicide bombers.

Troops are facing fierce resistance as militants retreat into the Old City, where street fighting is expected in the narrow alleyways and around the al Nuri mosque where ISIS declared its caliphate nearly three years ago.

A helicopter fired rockets into the area and heavy gunfire and mortar blasts echoed as troops fought in districts near the mosque, where ISIS's black jihadist flag hangs from its leaning minaret.

'Federal police and rapid response forces completely control the al-Basha mosque, al-Adala street and Bab al-Saray market inside the Old City,' a federal police spokesman said. 'Forces are trying to isolate the Old City area from all sides and then start an offensive from all sides.'

An ISIS attack on Thursday was halted when a vehicle was hit by a rocket in the Bab Tob old market area before it could approach federal police and other units, the rapid reponse force official said.

Five months into the campaign to liberate Mosul, ISIS's last major stronghold in the country, Iraqi forces backed by U.S.-led coalition air strikes have retaken the eastern half of the city and about half of the west across the Tigris river.

The fall of Mosul, Iraq's second city, would be a major setback for ISIS following months of losses in Iraq and neighbouring Syria. The city also holds huge symbolic significance for the terror group.

Federal Police Major General Haider Dhirgham said: 'It's important for them, it's where they declared their state [in 2014].'

Since launching their assault on the western sector, Iraqi forces have taken several districts and key buildings including the headquarters of Nineveh province's regional government and a railway station.

Carts loaded with bodies of civilians killed in air strike, are seen during a battle between Iraqi forces and Islamic State militants, in Mosul, on Friday

A father reacts after his son was killed in an airstrike, during a battle between Iraqi forces and Islamic State militants

Fleeing ISIS, Mosul's civilians cart out the dead from the city where fighting has been ongoing for five months

But the United Nations has warned that the exodus of tens of thousands of west Mosul residents could overwhelm aid groups trying to help them.

The last week has seen the highest level of displacement yet, with 32,000 displaced between March 12 and 15.

Many say food is running short and security is fragile even in liberated areas.

Lise Grande, the UN's humanitarian coordinator in Iraq, said. 'The number of people is higher than expected. If the pace accelerates further, it's going to stretch us to the breaking point.'

Iraq's Ministry of Migration and Displacement said more than 150,000 people had so far fled their homes in Mosul's west, with two-thirds taking refuge in camps near the city where they receive food, blankets and foam mattresses.

Ms Grande said the UN was concerned for the 600,000 people still trapped inside the city, forced to choose between staying amid the fighting or risking being targeted by jihadists if they decided to flee.

US officials have estimated that around 2,000 fighters remain inside the city.

'We fear the civilians there might be trapped in an extremely difficult situation,' she said.

The Reach Initiative, a group that helps aid groups collect data on humanitarian crises, said the situation in west Mosul was 'severe to extremely severe'.

'In areas still under (IS control), there is no access to markets and people are surviving on depleting food and water stocks, without access to electricity, fuel and healthcare,' it said.

In neighbouring Syria, three separate forces are advancing on the city of Raqqa, the main Syrian city under ISIS control.