The Islamist rebels said they executed the captive because talks with the Afghan authorities aimed at securing the release of the Christian aid workers in exchange for eight jailed insurgents had stalled.

The Taliban meanwhile freed a German journalist -- the third German to be kidnapped in a week in war-torn Afghanistan -- and his Afghan translator hours after abducting them in the east of the country, officials said.

"We killed one of the Koreans today because the government is not being honest in talks," Taliban spokesman Yousuf Ahmadi told AFP by telephone from an unknown location.

The head of the Afghan government delegation negotiating the release of the Koreans, Waheedullah Mujadadi, confirmed that the militant group had killed one of the South Korean hostages.

The Taliban also opened fire at him in a buffer zone between Taliban- and government-controlled areas, Mujadadi said. "I managed to escape the attack. They were trying to kidnap me as well or kill me," he said.

The militants -- who were ousted from power in Afghanistan by US-led forces in late 2001 -- set a deadline of 2030 GMT Wednesday for their demands for the release of eight jailed Taliban fighters to be met.

"We call on the South Korean government, parliament and its people to pressure the Afghan government to accept our demands or we'll kill more hostages after the deadline passes," Ahmadi said.

The government was unable to confirm a report by South Korea's Yonhap news agency, quoting an unidentified government official in Seoul, that eight of the hostages were freed Wednesday.

The hostages were to be moved to a safe zone and then flown back to South Korea after a medical check-up, Yonhap said. It later quoted a source as saying they were being taken to a US military base in Ghazni province.

South Korean and Afghan officials travelled to the insurgency-hit southern province where the Taliban are holding the hostages in order to lead the frantic efforts to save the hostages.

The Koreans are the biggest group of foreigners to be abducted during the Taliban's nearly six-year insurgency against the government of President Hamid Karzai and international forces in Afghanistan.

Any prisoner exchange would run counter to Karzai's pledge not to allow the practice after his government in March freed five Taliban militants in exchange for an Italian reporter.

A fresh hostage crisis was defused after a few hours when officials said Taliban rebels had freed the unidentified German reporter and his Afghan companion in eastern Afghanistan's Kunar province bordering Pakistan.

The pair were abducted early Wednesday from a house in the far-off district of Watapour where a NATO-led air strike killed several Afghan civilians some two weeks ago, provincial governor Shalizai Didar said.

"They were both freed with the mediation of tribal elders and other influential people. They are safe and sound," Didar told AFP.

The Taliban had earlier claimed responsibility for kidnapping the German journalist.

"They were freed with no conditions through the power and cooperation of peace-loving local elders," Didar said, adding that he was due to meet the German in the provincial capital later Wednesday.

Two other Germans were kidnapped in the south of the country last Wednesday.

The bullet-riddled body of one was dumped by a road on Sunday while the Taliban said the other was seriously ill and slipping in and out of consciousness due to diabetes.

The Taliban have demanded the release of 10 prisoners for the sick German and four other Afghan hostages, but have not set a deadline related to that group of captives.

The Taliban have previously called for South Korea and Germany to pull their troops out of the country but the issue has not figured in their most recent set of demands.