Taliban leaders are deciding what to do with 21 Korean hostages after Afghan President Hamid Karzai and US President George Bush ruled out making any concessions to free them, one of the kidnappers said on Tuesday.

"We know about their comments and will decide what to do next," said a Taliban commander who holds a group of four of the hostages. He said the Taliban leadership would make the decision on the fate of the Christian volunteers.

The commander, who declined to be named, said talks were still going on with South Korean diplomats in the region who are trying to secure the release of the 18 women and three men.

Speaking to Reuters by telephone from an undisclosed location, he repeated the Taliban line that Bush and Karzai would be held responsible for whatever happens to the Koreans if the Afghan government does not release jailed Taliban members.

Bush and Karzai, who met on Monday, have bluntly refused to meet the rebels' demands.

"Both leaders agreed that in negotiations for the release, there should be no quid pro quo for the hostages. The Taliban are brutal and should not be emboldened by this," White House spokesman Gordon Johndroe said.

In Seoul, where the South Korean government is under intense domestic pressure to secure the release of the hostages, their families issued a plea to Bush and Karzai to help free them.

"We sincerely ask you, with tears in our eyes, to understand the noble intention of the Korean volunteers who, despite all the dangers and difficulties, wanted to spread sharing and love in a place battered by poverty and conflicts," the said.

The kidnappers have already shot dead two male hostages and have repeatedly threatened to kill the rest of the captives if their demands are not met.

INVITED TO CONVERT

Taliban officials have said two of the female hostages were seriously ill, but South Korea's foreign minister said none of the captives were in a life-threatening condition.

"The hostages can't be perfectly healthy after nearly 20 days in captivity," the ministry quoted Song Min-soon as telling local reporters. But he added: "There are no signs of health problems that could pose a threat to their safety."

The Taliban commander said his group of hostages were well looked after and fed properly.

"They are given everything. potatoes, biscuits, tea, rice, fruit and Pepsi," he said. "They are taken out for fresh air and have the facility to take a bath."

The group had been invited to convert to Islam and the hostages told him they would study his offer.

"Again and again have invited them to become Muslims and they said they will deliberate on it," he said.

The Taliban snatched the group of 23 church volunteers from a bus in Ghazni province on the main road south from the capital Kabul on July 20.

The commander said the Koreans were held in an area of Ghazni that has been the scene of unprecedented violence in recent months, the worst since Taliban's overthrow in 2001.

Taliban militants have spread their influence northwards towards Kabul from their traditional southern strongholds.

Ghazni is an ethnically mixed province on the fringe of the Pashtun-dominated area to the south, where the largely Pashtun Taliban draw most of their support.

"The people of the area are cooperating with us," the commander said.

A senior official in Ghazni told Reuters that top provincial officials there had links with a pro-Taliban group and were adding to instability in the region.

The Taliban also had informers within the provincial security forces hampering any attempt at a rescue operation, a former Ghazni intelligence officer said.

People in Ghazni feel strong and growing frustration due to the lack of development and lack of rule of law in the province, local reporters and residents said.

That picture is repeated in many parts of the country, international aid workers say, adding to Taliban support.