Exploding shell - picture courtesy of KBS World
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Artillery fire on Korean border

North Korea has reportedly fired dozens of artillery shells across its western maritime border, prompting return fire from South Korea.

The South's military was placed on its highest non-wartime alert after the shells landed on Yeonpyeong island, killing two marines.

The North said it did not fire first in the incident.

John Sudworth explains the political implications of the incident.

Opening footage courtesy of KBS World

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