The Taleban claimed tonight that it had shot dead the second of its 23 South Korean hostages after the group's deadline expired for the Afghan Government to free its fighters from prison.

Yousuf Ahmadi, a spokesman for the Islamist extremist group, said that it had used an AK-47 assault rifle to shoot dead a hostage whom he named as Sung Sin.

Earlier today the body of the South Korean group's leader, 42-year-old Bae Hyung Kyu - the first hostage to be killed - arrived back in his home country after he was gunned down last week. The Taleban are still holding 21 other hostages, of whom 18 are women.

Hamid Karzai, the Afghan President, has described the hostage-takings as a "heinous act" and demanded that the Koreans are released.

"We set several deadlines and the Afghan government did not pay attention to our deadlines," Mr Ahmadi told the AFP news agency, disclosing the killing.

"Finally, tonight at 8.30 we killed one of the Koreans named Sung Sin with AK-47 gunshots."

The spokesman added that the body of the dead hostage had been dumped in the Qarabagh district of the southern province of Ghazni, the area where the devout Christians - who say that they were on an aid mission - were captured on July 19.

There was no independent confirmation of the death, with the South Korean embassy in Afghanistan refusing to comment on the latest developments.

Earlier the hardline Islamist militia extended an original deadline when it claimed it would start killing the hostages from 7.30am BST to 12.30pm.

The Taleban had demanded that the Afghan Government free Islamist extremists in its jails, but local negotiators said this was not up for discussion and called for two extra days to try to resolve the crisis.

The dramatic escalation of the hostage crisis - the largest Taleban kidnapping of foreigners since the US-led invasion of Afghanistan in 2001 - came on the day that Mr Karzai issued his first statement on the matter. In it, he criticised the kidnapping of "foreign guests," especially women, as contrary to the tenets of Islam.

"The perpetration of this heinous act on our soil is in total contempt of our Islamic and Afghan values," the President said, in a statement released after meeting a South Korean envoy in his Presidential palace this morning.

South Korea remained gripped by the unfolding saga today as the body of Mr Hyung Kyu was flown home.

Relatives of the remaining 22 hostages gathered at Saemmul Community Church in Bundang, just outside of Seoul, to say prayers, eat together and wait for news as 24-hour news channels played in the background.

Seo Jung-bae, 59, whose daughter and son are among the Christian volunteers, appealed to the Taleban for their release, saying: "Please, please send my children back so I can hold them in my arms. Our families are the same. Your family is precious, so is mine."

He added that the group had travelled to Afghanistan to help poverty-stricken Afghans in need. "They went there to help, thinking they (Afghans) are their friends," he said.

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