Police set up roadblocks after the attack on Lee Han Young, a relative of the North Korean leader, Kim Jong Il. The attack appeared to be in retaliation for the defection last week of Hwang Jang Yop, a senior North Korean politician, who is under police protection in the South Korean embassy in Peking.
Mr Lee was shot at close range by two men in the entrance of an apartment building on Saturday. Police said the gun used was a Belgian-made Browning, a standard weapon of North Korean agents. Neighbours who helped Mr Lee said he muttered "Spy, spy" before losing consciousness. Surgeons failed to remove a bullet from his head and last night he was given little chance of surviving.
The South Korean cabinet met to discuss the incident and offered 50m won (pounds 36,750) for information about the assailants. "North Korea has threatened to take hundred- and thousandfold revenge for the Hwang incident," said the Prime Minister, Lee Soo Sung. "This attack shows the threat is something concrete."
Mr Lee is the nephew of a former wife of Mr Kim, and escaped to South Korea in 1982. He had been under police protection and even had plastic surgery. The attempt on his life will raise anxiety in Seoul about the extent of North Korean infiltration. Since his own attempted defection last Wednesday, Mr Hwang, 73, a member of the North Korean Workers' Party central committee, is reported to have told South Korean interrogators that Pyongyang has 50,000 active spies in the South.
In Peking, groups of North Koreans continued to loiter outside the South Korean consulate building, where Mr Hwang was spending a fifth day. Pyongyang claims that he was kidnapped and one of its diplomats told reporters in Peking that "if the South uses force to move him to South Korea we will respond with force. We are determined to prevent them from taking him to the South."
Armed Chinese police laid spikes on the road in front of an anti-riot truck mounted with a water cannon.
In Pyongyang, celebrations went ahead for the 55th birthday of Mr Kim; the state media published the eulogies of the "Dear Leader" but made no mention of Mr Hwang's defection. "The Great General Kim Jong Il is trusted absolutely, eternally and fully as if he were god," said the Rodong Sinmun newspaper. "The Korean people regard him as their god because he defends the destiny of the motherland, nation and people." Celebrations included performances of dances and songs with titles like "Health to the Supreme Commander" and "Defend the Headquarters".
A North Korean diplomat in Peking said: "The Dear Leader is a pillar in our minds.
"Hwang, deep in his mind, will be thinking of this day and we believe he will celebrate it as well."