Two Vietnamese boys, aged 11, were killed and six children injured while they played with an old mortar shell they found on their way to school.

Village official Nguyen Sy Thong said Wednesday the shell was found in an area of central Vietnam which was used as an American base during the Vietnam War, AP reported.

After the war ended in 1975, it was converted to a military firing range.

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Thong said the boys found the old shell as they walked to school in the central highland province of Dak Nong, AP reported.

They picked it up and were playing with it when it exploded. Two boys died at hospital and their six classmates remain in a serious condition.

Police are investigating the tragedy.

There was a similar accident in December when a mortar shell, believed left from the Vietnam War, exploded in a south Vietnam village. Four children, aged four to 11, were killed and five others seriously injured, the Phuket Gazette reported at the time.