The group also questioned what South Korea had earned for its alliance with Washington in its anti-terrorism campaign. Seoul has sent troops to Afghanistan and Iraq.
Government steadfast
The calls come amid fears that rejecting the Taliban captors' demand for prisoner releases could lead to more killings after the latest deadline of midday Wednesday.
But 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.
Humayun Hamidzada, a spokesman for Hamid Karzai, the president, said: "As a principle, we shouldn't encourage kidnapping by accepting their demands."
In March, Karzai authorised the freeing of five captive Taliban fighters for the release of an Italian reporter, but called the trade a one-time deal.
The move was strongly criticised by the US and some European nations, with critics arguing it would be an incentive for the Taliban to stage more kidnappings.
'Un-Islamic'
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.
Seoul said it did not have the power to comply with the Taliban demands "because it doesn't have any effective means to influence decisions of the Afghan government".
"The Korean government strongly condemns and urges an immediate end to [the kidnappers'] heinous acts of killing innocent people in order to press for demands that it can't meet," the government said.
"The government makes it clear that it will not tolerate any further acts of harming innocent Koreans and holds the perpetrators responsible."
But the Taliban said more Korean hostages would die if its demands were not met by the deadline, noting that some of the prisoners it wanted released were held at the US base at Bagram.
The Organisation of the Islamic Conference on Tuesday added its weight to the calls for the release of the South Koreans, saying the act of kidnapping was "un-Islamic".
Judges killed
In a separate development, the bodies of four Afghan court officials kidnapped nearly two weeks ago have been found in the same province where Taliban fighters are holding the South Koreans.
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| The bound feet of two of the officials [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 Deh-yak district last night."