South Korean Christian activists held hostage by the Taliban said on Tuesday about half of the group of 23 church volunteers had left wills before leaving for Afghanistan.

A few had said Christian prayers in secret so as not to anger their Muslim captors, two of the former hostages told a news conference.

"We prayed, taking turns, pretending we were talking and with our eyes open" said Kim Ji-na, 32.

Kim was one of two hostages freed on Aug. 13, about two weeks before the remaining 19 hostages were released.

The group was kidnapped in Ghazni province in southeastern Afghanistan on July 19 as they were travelling in a tour bus. The Taliban shot dead two male hostages in the early stages of negotiations.

"I had drawn up a will," Kim said. She said it had been suggested to the group as part of preparations for the trip.

Kim had no comment on the criticism levelled against the church for taking inexperienced volunteers into an area where Taliban forces are strong.

The remaining 19 returned home to an uncomfortable welcome last Sunday, with many Koreans blaming them and the church that sent them for an ill-advised mission to an obvious danger spot.

Prior to the ordeal, the South Korean government had issued warnings about Afghanistan and worked to revoke visas for its evangelical Christian groups trying to send hundreds to the country. Seoul now bans its citizens from travelling there.

Kim said one of the two murdered by the Taliban had been taking a walk when a captor came for him, saying he was going home. His bullet-riddled body was found a day later in a ditch.

A doctor treating the group said many hostages were suffering from post-traumatic stress disorder but none showed signs of being severely beaten. All the former hostages are at a hospital in Anyang, south of Seoul.

A senior Taliban leader told Reuters last week that Seoul had paid $20 million for the hostages' release, but the South Korean government denies paying any ransom. It has been criticised internationally for striking a deal through direct negotiations.