BANGKOK (AP) — Police say workers at a scrap shop in Thailand’s capital accidentally detonated a large bomb believed to have been dropped during World War II, killing at least seven people and injuring 19 others.

Police bomb squad chief Kamthorn Auicharoen says construction workers found the bomb buried at a building site and sold it to the scrap shop in northern Bangkok.

He said workers at the shop were using a blowtorch to take the bomb apart when it exploded Wednesday.

The massive blast ripped apart the scrap shop in Bangkok’s Lad Plakao neighborhood and damaged nearby houses.

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