The Taliban sought guarantees of safety from the U.N. mission in Afghanistan should their delegation hold talks with South Korean officials in government-controlled territory over the hostage crisis, a purported militant spokesman said Friday.

The offer came as Amnesty International said it directly appealed to the Taliban to free 21 South Korean hostages, warning the militant movement that holding and killing captives is a war crime.

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Qari Yousef Ahmadi, a purported spokesman who claims to speak for the Taliban, said that the militants are ready to negotiate about the freedom of the captives with South Korea's ambassador to Afghanistan anywhere if the U.N. mission guarantees the militant delegation's safety.

"The Taliban are ready to meet them in Kabul, other cities or other country, but only under one condition and that is that the U.N. guarantees their safety," Ahmadi said, speaking on a phone from an undisclosed location.

Officials from the U.N. mission in Afghanistan were not immediately available to comment on Ahmadi's offer.

Amnesty, meanwhile, said it made the appeal for the South Koreans freedom in a phone call to Ahmadi on Thursday.

"Hostage taking and the killing of hostages are war crimes and their perpetrators must be brought to justice," Irene Khan, secretary-general of the London-based group, said in a statement.

Ahmadi told Amnesty that "we are trying to resolve this issue ... acceptably," but did not agree to protect the hostages from harm and release them immediately, the statement said.

The renewed attempts for freeing the captives, who include 16 women and five men, came as South Korean lawmakers went to Washington to urge the United States to help end the hostage crisis.

The Taliban have already shot and killed two men in the group, which was doing voluntary health work in Afghanistan. They were abducted on July 19 in Ghazni province as they traveled by bus from Kabul to Kandahar.

Richard Boucher, assistant U.S. secretary of state for South and Central Asia, said Thursday the use of military force to free the hostages had not been ruled out.

"All pressures need to be applied to the Taliban to get them to release these hostages," said Boucher. "There are things that we say, things that others say, things that are done and said within Afghan society, as well as potential military pressures."

Afghan officials said Taliban captors agreed to meet with South Korea's ambassador to Afghanistan, but they had not yet agreed on a venue.

"If the Taliban want to come to the area where we are for the sake of these hostages, 100 percent, they will be safe," Ghazni Gov. Marajudin Pathan told a news conference Thursday.

But both sides have proposed places that could put them at risk -- including the office of the provincial reconstruction team, which is run by international troops.

"The Koreans told the Taliban to come to the PRT, and the Taliban told the Koreans to come to their base," Pathan told The Associated Press after the news conference.

Taliban's Ahmadi said the remaining 21 hostages were still alive, but that two of the women were very sick and could die.

A group of local doctors, meanwhile, traveled from Kabul to Ghazni in a hope of being able to reach the hostages, and treat those in need of medical care.

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