The man is identified as Shim Sung-Min, a former infotech worker.
The Afghan government has refused to free Taliban prisoners, saying it would only encourage further abductions.
Douglas Shin, a South Korean pastor, told Al Jazeera: “They did their preparation for the trip. But they could have had a lower profile than using a tourist bus to travel the Kabul-Kandahar road.”
“But it also believes that it would be worthwhile to use flexibility in the cause of saving the precious lives of those still in captivity.”
A South Korean civic group criticised the US for refusing to get more involved in the standoff, saying it was as if the US was watching “a fire across a river”.
The Afghan government explicitly said for the first time on Tuesday that it would not release Taliban prisoners – the group’s chief demand to free the captives.
In March, Karzai authorised the freeing of five Taliban fighters for the release of an Italian reporter, but called the exchange a one-time deal.
Tom Casey, a spokesman for the US state department, said there was regular contact between US and South Korean officials on the standoff, but would not comment on specifics.
Afghan judges killed
In a separate development, the bodies of four Afghan judges kidnapped nearly two weeks ago have been found in the same province where Taliban fighters are holding the South Koreans.
|The bound feet of two of the judges [AFP]|
A photographer for Agence France-Presse, the French news agency, said he had seen the bodies of the four men.
He said one had been shot in the head, the others in the body, and that their feet had been bound.
Police said the bodies had been dumped in a village in the southern Ghazni province.
The Taliban had claimed to have kidnapped the four but did not immediately confirm it was responsible for their murder.
Mohammad Zaman, a deputy police chief, said the men were judges from the neighbouring province of Paktika.
He said: “They were killed and their bodies were found in Dehyak district last night.”