A security official in Myanmar says a mortar round left over from World War II has exploded accidentally in the country's second city, killing a 12-year-old boy and two other people.

The official said the blast occurred Monday in Mandalay as it was being dismantled for scrap metal at a smelting plant.

The official spoke on condition of anonymity because he was not authorized to speak to the media.

Bombs from the war are still found in Myanmar from time to time.

In September, seven people were reported killed when World War II ordnance they found in a river in the west of the country exploded.