Balanced on the edge of the heap of rubble, the digger struggles to clear the concrete blocks and twisted metal rods.

With snipers lurking on rooftops and bombs hidden in the rubble, rescue workers are risking their lives in a desperate search for civilians buried during the battle for Iraq's Mosul.

Overwhelmed by a blazing sun and an unfathomable grief, Abdulrahman Mohammed and his brother Ammar smoke cigarettes in front of a digger as the workers clear through a mountain of debris in a cloud of dust.

The bodies of their brother Ahmed and his family, who disappeared while fleeing fierce fighting between Iraqi forces and jihadists in west Mosul, are believed to be trapped underneath.

After eliminating the last snipers of the Islamic State group lying in wait nearby, security forces on Tuesday allowed rescuers to tackle the debris.

But after such a long wait, there is little hope of finding survivors without a miracle.

“They've been buried for about three weeks, a whole family. It's a tragedy,” Ammar says.

Abdulrahman thinks it is still possible that Ahmed and his family might have left the house before the bombardment.

“Our only hope is that we don't find them here,” he says.

On June 6, the Iraqi army advanced inside the Zanjili district, where many civilians were trapped in their homes by order of IS.

'Mosul's the worst'

Exhausted and hungry, some seized the chance to try to escape, including Ahmed, his wife and their six children.

But the family saw IS fighters coming and "took refuge with about 30 other civilians in the basement of a neighbouring house," says Abdulrahman.

Inside, the group was desperately thirsty. A man volunteered to fetch water. On the way, a sniper's bullet went through his cheek. Wounded, he did not return.

Minutes later, the house was hit by aerial bombardment that people in the neighbourhood blamed on the US-led coalition supporting Iraqi troops on the ground against the jihadists.

“Maybe they made a mistake with the house or they bombed it because there were IS snipers on the roof,” Abdulrahman says.

The survivor told the two brothers, who alerted the civil defence, a unit within the interior ministry that has also helped victims in other parts of Iraq in recent years as the government retakes territory from IS.

Their job: to rescue the living and collect the dead so they can be buried with dignity.

“We did Fallujah, Ramadi... But Mosul's the worst,” says Major Saad Nawzad Rasheed.

His men sometimes arrive in time to save lives. Other times they are too late, hindered by snipers and makeshift bombs.

'Too dangerous to dig'

“I've never seen so much destruction -- women and children affected -- all because of these dogs,” Rasheed says, referring to the jihadists.

Balanced on the edge of the heap of rubble, the digger struggles to clear the concrete blocks and twisted metal rods.

After more than an hour at work, objects appear at the bottom of a hole several metres deep, including two children's dolls.

After one more strike by the digger, a rescuer shouts: "Stop!"

Abdulrahman and Ammar approach. There are no traces of their relatives at the bottom. But a little higher up there is an unexploded rocket, threatening to fall.

The excavator will not dig any more, especially since the army has just discovered two car bombs in the vicinity, one of which is less than 50 metres away.

“It's too dangerous to dig in these conditions. We'll let the army clear any bombs first,” Rasheed says.

That means a delay of at least two days.

It is a crushing blow for the brothers.

But Abdulrahman still holds out hope.

"Maybe they fled to the Old City," he says, pointing to the warren of alleyways from which black smoke rises on the horizon as Iraqi forces try to flush out jihadists holed up among tens of thousands of trapped civilians.