Cambodian authorities have temporarily closed a school after thousands of pieces of unexploded ordnance from the country’s nearly three decades of civil war were unearthed.

The ordnance was found at Queen Kosamak high school in the north-eastern province of Kratie after deminers were invited to search for buried landmines on the campus before a new building was constructed, said Chheang Heng, the provincial deputy chief for education.

The site was an ammunition warehouse during the Khmer Rouge regime in the 1970s before being turned into a school and all of the ordnance was thought to have been removed, he said.

Between Friday and Sunday, 2,116 pieces of ordnance were collected by deminers from the Cambodian Mine Action Centre, the government agency’s director-general, Heng Ratana, posted on Facebook.

They included M79 grenades, FuzeM48 shells and ordnance for the B40 rocket launcher.

Photos posted on its Facebook page showed the dirt-covered items placed in a row in the school grounds.

Heng Ratana said many more pieces of ordnance are believed to still be buried, so the school, which has more than 1,000 students, will be closed for some days while the deminers work to collect the dangerous material.

“I know that this school site used to be a big ammunition warehouse of the Khmer Rouge in late 1970s, but I could not believe that there was a huge amount of ammunition buried underground like this,” Chheang Heng said.

“How many casualties would have happened if this ammunition exploded?”

The brutal rule of the radical communist Khmer Rouge was blamed for the deaths of an estimated 1.7 million Cambodian from starvation, illness and killing before being ousted by a Vietnamese invasion.

Three decades of war finally ended in the late 1990s but left Cambodia littered with an estimated four million to six million landmines and other ordnance.

Most has been cleared but the explosives continue to kill people.

Since the end of the fighting, nearly 20,000 people have been killed and some 45,000 injured by leftover war explosives, although the average annual death toll has dropped from several thousand to less than 100.

Three members of a local demining team were killed by a leftover anti-tank mine as they were working in northern Preah Vihear province in early 2022.

The Cambodian government aims to clear all the nation’s leftover land mines and unexploded ordnance by 2025.