The Taliban has said it has not killed any more of its captives, after already shooting dead two, as it was holding out for direct talks with South Korean officials who, they said, had given assurances that Taliban prisoners could be released.

The release of Taliban prisoners has been the key demand of the extremists, who kidnapped the group of Christian aid workers, most of whom are women, on July 19 as they travelled in the country's insurgency-hit south.

Presidential spokesman Cheon Ho-Seon said there was a direct line of communication between government negotiators and the militia, but he made it clear that Seoul could not respond unilaterally to Taliban demands.

"The Korean government is not in a position to give a direct answer to the Taliban's demand that its prisoners be swapped for Korean hostages," he said.

The Afghan government has refused to release Taliban fighters for fear of encouraging kidnapping, and after severe criticism from the United States over a similar deal in March.

Afghan provincial officials and the Taliban have said there were plans for a face-to-face meeting between the militia and a South Korean delegation, though no confirmation has come from the South Korean embassy in Afghanistan.

South Korea's Yonhap news agency however cited "informed sources" saying that as most of the hostages were ill, including two women reportedly in serious condition, the talks were likely to be held later Friday.