KANDAHAR, Afghanistan - Taliban rebels in Afghanistan on Sunday gave 23 South Korean hostages a day's reprieve, extending a deadline by which they threatened to kill the captives if their demands were not met.

A man holds the South Korean newspaper Chosun Ilbo which displays on their front page an image of a group of South Korean Christians posing for a commemorative photograph before leaving for Afghanistan on 13 July. [AFP]

The Islamic militants announced the 24-hour extension as frantic talks dragged on into the night to save the aid workers, warning however that the hostages would be killed if nearby Afghan forces tried to storm their hideout.

The guerilla fighters have demanded that Kabul free 23 jailed Taliban in return for the hostages, and that South Korea withdraw its 200 troops serving under US-led command in the war-torn country.

"We have extended the deadline by 24 hours, which will last until tomorrow at 7:00 pm (1430 GMT Monday)," Taliban spokesman Yousuf Ahmadi told AFP minutes after the earlier limit expired.

"The talks continue," he said in a telephone call from an unknown location, without providing further detail.

Fears for the captives, mostly women in their 20s and 30s abducted last Thursday in southern Afghanistan, rose after police recovered the body of a German engineer.

The Taliban earlier said it had killed two Germans abducted a day before the South Koreans, but Kabul and Berlin insisted one of them was still alive.

A South Korean crisis team Sunday flew into Kabul to spearhead efforts to save its nationals, while Seoul reaffirmed that it would withdraw its troops from Afghanistan by year's end as it had already planned.

The double hostage crisis is the latest in a series of abductions targeting the 37 countries with forces in Afghanistan. The Taliban have also demanded that the 3,000 German troops stationed in the country be sent home.

The Afghan defence ministry said its forces, backed by the US-led coalition, had taken up positions in the Qara Bagh district of southern Ghazni province, where the Koreans were being "held in the hands of enemies of the people."

The troops were "awaiting attack orders," the ministry said in a statement. "Whenever the authorities consider it appropriate they'll launch the offensive."

The US-led coalition denied it had so far been asked to help.

The military pressure on the Taliban came despite talks between authorities and the rebels, brokered through local tribal elders and religious leaders.

"I hope we get good results," said provincial police chief Alishah Ahmadzai.

The South Koreans, who were on an aid mission, were seized Thursday while travelling by bus along the highway linking southern Kandahar -- the birthplace of the Taliban -- and Kabul.

The hostages -- members of the Saem-Mul Protestant Community Church in Bundang, on Seoul's outskirts -- are the biggest group of foreigners to be kidnapped in Afghanistan since the fall of the Taliban regime in 2001.

The Germans were kidnapped Wednesday along with five Afghans, and a Taliban spokesman on Sunday reaffirmed claims that the rebels had killed all of them after Berlin and Kabul failed to meet tight deadlines for talks.

"We have recovered the body of one German," said Hewas Mohammad Muslim, the police chief of the southern province of Wardak, without specifying the cause of death. "That is all I know at this point."

An interior ministry source said the German's body had "several bullet wounds to the head," but this was not officially confirmed.

The source added, however, that one of the five Afghans had actually been freed, possibly to deliver the corpse to authorities.

Afghanistan's foreign ministry and German Foreign Minister Frank-Walter Steinmeier said late Saturday that they still thought one German was alive.

The other had died "due to the conditions of detention imposed by his captors" but had not been murdered, Steinmeier said, while the Afghan ministry said the German had died of a heart attack.

The private Pajwhok news agency reported that an Afghan hostage who escaped earlier Sunday told interior ministry officials the other German was still alive, but this could not be immediately confirmed by officials.