A firefight broke out earlier today across one of the last remaining frontiers of the Cold War - the aggressively fortified Demilitarized Zone that separates South Korea from its hardline communist neighbour to the north.

The brief bursts of machinegun fire from guards on both sides of the border were the first “hot” exchange along the DMZ for just over a year.

The border, which comprises a wide strip of land peppered with landmines, razor wire and tank traps, divides two countries which, despite a 50-year armistice, are still technically at war.

Over the years the DMZ has been the scene of several firefights, some involving casualties, but incidents have become much rarer since an era of limited rapprochement began in 2000. North Korea still does not recognise the DMZ, a line drawn unilaterally by the United Nations Command in 1953, as legitimate.

The skirmish comes amid conflicting signs from the regime of Kim Jong Il. On the one hand there is growing optimism in Washington that the enigmatic dictator may be persuaded to abandon his nuclear weapons; but recent summit talks between Seoul and Pyongyang aimed at easing military tension along the DMZ ended in deadlock.

The two Koreas have been unable to agree on the re-drawing of a maritime extension of the DMZ, and new guidelines to prevent skirmishes at sea.

Last week Pyongyang, protesting South Korea’s upcoming joint military exercise with the US, snubbed an offer from Seoul to join it in anniversary celebrations of Korea’s liberation from Japanese rule.

Today’s exchange began when North Korean soldiers guarding their side of the DMZ at Inje - about 100 miles from Seoul - fired a few dozen rounds across the border. Soldiers in the south responded with a volley of 10 shots fired into the North and blared a message over huge loudspeakers demanding an apology. No injuries have been reported among the guards in the South, but it is not known whether any of their counterparts to the North were hurt or killed.

Seoul said that it was still trying to establish the cause of the firefight - accidental bursts of gunfire are not uncommon. The most recent such battle, on July 31 last year, also produced no known casualties.

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