A two-minute skirmish on the Yellow Sea border thrust North and South Korea into direct naval conflict with each other for the first time in seven years.

The suddenness of the exchange, and details of the North Korean ship’s behaviour beforehand, suggest that the engagement may have been a deliberate gambit by Pyongyang: a ploy to ratchet paranoia before President Obama’s visit to Seoul next week and to set the nuclear negotiating table on Kim Jong Il’s terms.

The North Korean vessel left the scene in flames after sustaining long-range fire from its South Korean counterpart. Neither side appears to have sustained heavy casualties, although the final status of the North Korean ship remains unknown and some reports suggest that at least one sailor may be dead.

The region where the battle took place has been a persistent source of trouble. It is supposedly split by the northern limit line (NLL) — a disputed maritime extension of the demilitarised zone that divides North from South and represents the most heavily armed border on the planet. It was along this line in 1999 and 2002 that the two Koreas clashed previously.

The skirmish began yesterday morning when a North Korean patrol boat crossed the NLL in defiance of several warning signals from a South Korean naval craft. With 3km of clear water separating the ships, the North Koreans launched a volley of fire at the South Korean vessel, which returned heavier fire.

Kim Tae Young, South Korea’s Defence Minister, said that the motive needed to be clarified but suggested that it was not accidental, given that the North Korean boat retained communications with its command. “But on the other hand, it is not easy to conclude that a provocation would be conducted with only one ship,” he told parliament.

Political and defence analysts said that it would probably not derail recent progress as long as North Korea was still interested in talks.

Until yesterday it appeared that there might be scope for a period of level-headedness after what has been an acrimonious six months. In May North Korea’s tests of long-range missiles and nuclear weapons left disarmament talks in tatters.

The North Korean state news agency account of the skirmish described how a flotilla of South Korean warships running north across the border in an assault which was repelled by “a prompt retaliatory blow at the provokers”.

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