An explosion at a South Korean weapons testing range close to the heavily-fortified border with North Korea has killed one person and injured at least five others, officials have said.

The blast occurred on Thursday morning at the Pocheon bomb testing site, north of the South Korean capital, Seoul.

Three of the wounded are said to have suffered serious injuries, a defence ministry official told Al Jazeera.

The cause of the explosion is under investigation.

Researchers were testing an experimental explosive when the bomb blew up, a spokesman for South Korea's state-run Agency for Defence Development said.