South Korean presidential spokesman Cheon Ho-Seon said there was a direct line of communication between South Korean negotiators and the militants, but he said that Seoul cannot respond unilaterally to Taliban demands.
The Taliban wants the Afghan government to release at least eight imprisoned militants in exchange for the lives of the Christian aid workers. Kabul has rejected the demand, saying that a prisoner exchange would only encourage more kidnappings.
Afghan officials are reportedly searching for a place inside Afghanistan where South Korean negotiators can safely meet the Taliban insurgents to negotiate. The Taliban has declined to meet at a venue under the control of NATO-led forces.
South Korea has asked the Afghan government to show "flexibility" in dealing with the crisis, and has urged the United States to help free the hostages.
The Taliban today refused to allow an Afghan medical team access to the hostages. The militants said they would free "two seriously ill" female hostages only if the government released two Taliban prisoners.
The Taliban militants have killed two captives since kidnapping the group of 23 South Koreans in central Ghazni Province on July 19.
(compiled from agency reports)