South Korea's foreign minister on Tuesday denied reports that two of the 21 Korean hostages held by Taliban insurgents in Afghanistan were dangerously ill.

"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."

Taliban officials have said two of their 18 female hostages are seriously ill. They have killed two male hostages and are still holding another three men.

The kidnappers are demanding Afghan President Hamid Karzai and U.S. President George W. Bush, who met at the Camp David retreat in Maryland on Monday, free jailed rebels or be responsible for the deaths of the Korean hostages.

In Seoul, their families issued a plea to Bush and Karzai to help free the hostages.

"We do not want world order and principles to be undermined for the sake of the release and safe return of the Koreans. Saving these people, however, will also serve as an opportunity to reaffirm the precious values of humanity as a whole," they said.

"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."

CHURCH CRITICISED

The hostages were all members of the same Christian church who had gone into Afghanistan to provide aid. The church leaders have been criticised at home for taking young and inexperienced members into a known danger spot.

The South Korean government is under intense domestic pressure to secure the release of the hostages but concedes there is little it can do to meet the kidnappers' demands in the face of a blunt refusal by both the Afghan and U.S. governments to meet the Taliban 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.

South Korea has proposed holding face-to-face talks with the Taliban as a way of breaking the impasse, but the two sides have not been able to agree on a venue for the discussions.

There have been numerous rallies and candlelight vigils throughout South Korea since the kidnapping, some calling for the United States to intervene.

About 100 peace activists held a rally in central Seoul on Tuesday.

"I feel concerned that people are getting cynical on the issue because they think this crisis is based on religious or political differences. However, the most important thing is to gather our hearts to free the hostages," said Choi Seung-kook, secretary general of Green Korea United, one of the organisers of the rally.