The Taliban has killed one of the 23 South Korean hostages kidnapped in Afghanistan, according to a spokesman for the hardline Islamic group.

It had threatened to start murdering the hostages unless its demands for the release of Taliban prisoners were met.

The South Korean Christians were seized in Ghazni province, south of the capital Kabul.

Taliban spokesman Qari Mohammad Yousuf said: "We had assurance from the Koreans that Kabul will release Taliban prisoners in batches and we will reciprocate.

"We gave them eight Taliban names and they should have been freed by 7pm (2.30pm UK time) yesterday, but nothing happened.

"The Koreans should put pressure on Kabul on this for there is the risk that at any moment, any time something can happen to the hostages."

He added: "If by two o'clock today (9.30am UK time), the Taliban are not freed, then some of them will probably be killed. Our patience is running out."

Next month, representatives from Afghanistan and Pakistan will meet to discuss plans to counter the growing Taliban threat that has sharply strained ties between the already uneasy neighbours.

Afghan President Hamid Karzai and Pakistani leader Pervez Musharraf will address the four-day jirga, or grand assembly, which starts on August 9.

The two countries have drawn up a participants list totalling 700, including religious clerics, politicians, writers and tribal elders.