KHARTOUM (Reuters) -The bespectacled, grey-bearded man ran out of the primary school in Khartoum's Amarat district, shaking with shock.

He, like thousands of others, had returned to check on buildings retaken by the army after two years of civil war, only to find a new threat lurking in the rubble of Sudan's capital, in his case an unexploded shell under a pile of old cloth.

"I'm terrified. I don't know what to do," Abdelaziz Ali, 62, said outside the school where he used to work as an administrator before the conflict started in April 2023 and the Rapid Support Forces paramilitaries moved in.

"It's around 40 cm (16 inches) long – looks like anti-armor. This is a children's school."

Ammunition and missiles litter streets, homes, schools and shops across the city where families have started to return to the buildings that the RSF commandeered.

Sudanese and U.N. clearance teams are out checking, trying to make things safe. But they say they need more staff and funds, particularly since the U.S. aid cuts.

In Amarat, Ali pointed at other shells on the dirt road between the school and a kindergarten. Several missiles were seen lodged in crushed vehicles.

A caretaker from another building said authorities had found and removed ammunition and drones in the basement. But the anti-tank missiles were still there.

"We're afraid one explosion could bring the whole place down," he said.

More than 100,000 people have returned since the army took back control of Khartoum, and most of central Sudan, in a conflict that started over plans to integrate the military and the RSF.

The RSF still holds huge swaths of western Sudan and has switched tactics from ground incursions to drone attacks on infrastructure in army-held areas.

'IT EXPLODED WITHOUT WARNING'

Sudan's National Mine Action Centre said more than 12,000 devices have been destroyed over the course of the war. Another 5,000 have been discovered since operations expanded into newly re-taken territory, director Major General Khaled Hamdan said.

At least 16 civilians have been reported killed and dozens more wounded in munitions explosions in recent weeks. The real toll is feared to be higher.

"We only have five working teams in Khartoum right now," said Jamal al-Bushra, who heads the centre's de-mining efforts in the capital, focusing on key roads, government buildings and medical centres in downtown Khartoum, the site of the heaviest fighting.

"We need $90 million just to start proper de-mining and surveying operations," Hamdan said.

Crews pick up shells by hand and carefully place them into old suitcases and boxes, or side by side on the back of a pick-up truck, cushioned from the metal sides by a layer of dirt.

Volunteer groups have taken up some of the work.

"We've dealt with more than ten live shells today alone," said Helow Abdullah, head of one team working in the Umbada neighbourhood of Khartoum's twin city Omdurman.

The United Nations Mine Action Programme nearly closed its doors in March after U.S. funding cuts, until Canada stepped in to support it.

"We need hundreds of teams. We have just a handful," Sediq Rashid, the programme's head in Sudan, said. Work has also been hampered by problems getting travel permits, he added.

"It's very worrying because these areas need to be checked (by) a professional team ... And then (people return)," he said.

Rashid said the de-mining teams have barely scratched the surface, particularly in areas outside Khartoum that were also heavily affected.

Without the proper sweeps, residents are left to fend for themselves.

Sixteen-year-old Muazar lost his left arm and suffered severe wounds when a shell exploded while his family was clearing rubble in their home on Tuti Island where the Blue Nile and the White Nile meet in Khartoum.

"It was a 23 mm anti-aircraft round. It exploded without warning. The blast was two metres wide," Muazar's uncle said, standing by the boy's hospital bed in Omdurman.

(Reporting by Khalid Abdelaziz, Eltayeb Siddig and Nafisa Eltahir, writing by Mohamed Ezz and Nafisa Eltahir; Editing by Andrew Heavens)