The world's most heavily guarded frontier, the line that divides North and South Korea, is the focus of renewed tensions with confrontation looming on several fronts. From 1 December, the secretive North Korean leadership will close the land border between the Koreas at the few places where there are still openings.
The move is retaliation for hostile propaganda, notably the dropping of leaflets from hot-air balloons launched by South Korean civic groups with messages supposedly denigrating Kim Jong-il, the North Korean leader, and his despotic rule. Pyongyang is also stopping UN nuclear inspectors from taking soil and nuclear waste samples from its nuclear plant at Yongbyon.
The crossing closing is all the more significant because of intelligence reports suggesting that Mr Kim suffered a stroke in August which left him half-paralysed after brain surgery. Seeking to show that the Dear Leader is, on the contrary, in good health, the North Korean media claimed this week that he had attended two dramatic performances staged by the army and the navy, and waved cheerily to the actors.
Since no pictures were shown of Mr Kim enjoying North Korea's military arts festival, the effort to establish that he is healthy is proving counter-productive. When pictures have been released, it is unclear when and where they were taken.
Nobody expects another war but North Korea's very weakness is threatening. Its leadership, mysterious in its composition and strategy, has few cards in its hands. International attention focuses on its nuclear weapons, primitive though they may be. But without its nuclear programme the North, impoverished and ruined, has no bargaining strength. It may see the election of Barack Obama in the US as presenting opportunities that are not there. Its threats carry a certain weight because it is too weak to retreat from them.
The border between the Koreas has remained so heavily militarised even during periods when relations were less sour, that there is not much that either side need do to strengthen defences. On the southern side of the border, the banks of the Imjin river, where it faces North Korea, 40 miles north of the capital Seoul, are dotted with guardposts and high barbed-wire fences; further back are long-established military bases. The demilitarised zone (DMZ) around the village of Panmunjom was for long one of the showpieces of the Cold War, and to a great degree it still is. Signposts show where North Korean tunnels under the DMZ were discovered. From an outpost called Dora Observatory, Sergeant O Ti Wan of the South Korean army points to the North Korean city of Kaesong, overlooked by a tower which "stops all radio and television transmissions from the South".
Outside Qaesong are white buildings in the far distance which at one time promised to be one of the more hopeful signs of North-South co-operation. This was the establishment of a joint industrial zone where 35,000 workers from North Korea and 1,500 managers from the South, produce simple goods including pots and pans, watches and agricultural machinery. As we watched, a long convoy drove south out of the industrial zone carrying workers and finished goods.
But the zone may soon be abandoned. South Korean government officials were forced to leave in the summer, and last week the North said it would shut its border tight from 1 December. The North may also be reacting to the tougher stance towards it taken by the South Korean President Lee Mung-bak since he was elected in February. But the more conciliatory line taken by his predecessors never achieved much. A symbol is Dorasan station which opened in 2002 and was meant to link with North Korea. Its walls are covered with vivid signs of wraith-like hands grasping each other in friendship. A map shows the station as the first stop on a railway that would reach Peking and link with the trans-Siberian. Only one train uses the station, taking goods to and from an industrial zone a couple of miles away.
South of the DMZ, the rocky hills and glens are being rapidly suburbanised. The site of the last stand of the 1st Gloucestershire Regiment, the "Glorious Glosters", surrounded and forced to surrender after suffering heavy casualties and running out of ammunition in a three-day battle with the Chinese Army in April 1951, is in a narrow valley just south of the Imjin. Once an idyllic spot fenced in by steep hills, it now resounds to the echoes of rock being smashed as a new road is constructed immediately overlooking the memorial.
Kim Jong-Il: The lost leader
9 September Kim Jong-Il fails to attend military parade marking the 60th anniversary of North Korea's founding, prompting rumours that he suffered a possible stroke. He had not been seen in public since 14 August
31 October Absent from funeral of Pak Song Chol, honorary vice-president of Presidium of the Supreme People's Assembly
2 November Official photos are released reportedly depicting Mr Kim at a student football match on the 62nd anniversary of Kim Il-Sung university, named after his father, the country's founder
5 November Official state media release new photographs reportedly showing Mr Kim posing for photographs during a visit to military units
16 November More pictures issued purportedly showing Mr Kim at a military art festival
Korea in numbers
2m Troops are stationed on both sides of the Demilitarised Zone (DMZ)
28,000 American troops deployed in South Korea, with many guarding the DMZ
49.05m Population of South Korea
23.3m Population of North Korea