The Education Ministry has written to all city and provincial education departments telling them to stop using unexploded bombs as school bells.
A ministry letter said that in the past some schools had used live ordnance as a signal to students.
Education Minister Hang Chuon Naron wrote that the guidance had come from the Cambodian Mine Action and Victim Assistance Authority, which said all kinds of munitions could cause accidents at any time.
“Stop using unexploded ordnance as a bell in school to avoid accidents to Cambodian children because anything could happen,” Mr Naron said.
Thon Tharin, president of the Kampong Speu provincial education department, said his department got the letter and had sent it out to all schools for implementation.
He said that in the past, some schools had used unexploded ordnance as a bell to let students know the start and end of the school day and when to take breaks.
However, this was rare now, he said. Schools now use truck wheels to strike or electric bells instead.
He said that there had not been any accidents involving students, but the letter from the ministry was important because officials were afraid there could be a serious incident.
The Cambodia Mine Action and Victim Assistance Authourity issued a report recently saying there had been 39 accidents in 2017, a 46 percent decrease on the 72 accidents in 2016.
Since 1979, a total of 64,720 casualties have been recorded by the Cambodia Mine Victim Information System.
Heng Ratana, director-general of the Cambodian Mine Action Centre, said earlier that the centre received $1.2 million from the United Nation Development Programme for a one-year mine clearance project in three provinces this year.
He said the governments of Canada, Australia and Switzerland were supporting a project to remove mines in Pailin, Battambang and Banteay Meanchey provinces.
Under this project, the Cambodian Mine Action Centre plans to demine a total of 7,500,000 square metres of land.