Cambodia's government has told schools across the country to stop converting war-era ordnance into school bells to prevent possible explosions.
Nearly three decades of civil war and US bombing starting in the 1960s left Cambodia one of the most heavily bombed and mined countries in the world.
Turning bombs or shells into bells was a widespread practice immediately after the fall of the Khmer Rouge in 1979, when Cambodia's education system was destroyed and teachers used any material available.
The shells are normally deactivated by the time they are put into use.
But education minister Hang Chuon Naron said demining authorities advised him risks still remained when the bells are struck or in the process of being repurposed.
Education authorities must inform all schools to "stop taking unexploded ordnance to be improvised as bells", he said in a letter seen by AFP on Wednesday.
There no known reports of the bells exploding, but children have been killed in blasts on school grounds after playing with other kinds of dug-up ordnance such as grenades and landmines.
In January last year thousands of Cambodian villagers were evacuated after two US tear gas barrel bombs from the Vietnam war era were found near a primary school in Svay Vieng province.
Heng Ratana, director of Cambodian's Mine Action Centre, told AFP the ministry's move was an extra step of caution.
"We don't allow them to use because some (deactivated) bombs may still have fuse inside and when we hit it, the bomb might explode," he said.
He said it would also help "end confusion" among children, who may also try to strike unexploded ordnance when they find it in day-to-day life because they saw teachers hit the bell at school.
Unexploded ordnance has killed around 20,000 people and maimed tens of thousands of others since 1979, though rates have declined significantly and a number of demining organisations operate in the country.