The blood-stained body of the bespectacled man was dumped in a field of clover beside a road in Arzoo, a village some 10 km (6 miles) from the eastern city of Ghazni.

"If the Kabul administration and Korean government do not give a positive reply to our demand about the release of Taliban prisoners by tomorrow 1200 (local time), then we will start killing other hostages," Taliban spokesman Qari Mohammad Yousuf told Reuters by telephone from an unknown location.

President Hamid Karzai's spokesman said bowing to Taliban demands would encourage more kidnapping, adding "we are doing what is the best for the interests of the hostages, and government".

Karzai came under harsh criticism in March for releasing a group of Taliban prisoners in exchange for an Italian journalist.

Taliban spokesman Yousuf said Afghan negotiators had not contacted the Taliban since the second hostage was killed on Monday and said the insurgents suspected the Afghan government and foreign troops were planning a rescue bid.

Any attempt to rescue the hostages by force would put the Koreans' lives at risk, he said.

The victim was identified as Shim Sung-min, 29, a former employee of an IT firm who did volunteer work to help the poor. He was shot after the expiry of other deadlines the Taliban had set for the release of rebel prisoners.

Body Recovered

Police recovered his body from Arzoo, some 80 km (50 miles) from where the group of 18 women and five men were seized near Qarabagh on the main road south from Kabul. The distance between the two places undermines government claims the kidnappers are surrounded.

On Wednesday, the Taliban killed the leader of the group.

Negotiations are deadlocked with Afghan authorities seeking the release of the 18 women before any prisoners are freed and the kidnappers insisting its fighters be let out of jail first, a Western security analyst said.

US State Department deputy spokesman Tom Casey said the hostages were "innocent people who certainly have no party to any of the conflicts in Afghanistan and it's again representative of the viciousness of the Taliban that they're engaged in this".

The crisis has focused attention on growing lawlessness in Afghanistan, where Taliban influence and attacks are spreading to areas previously considered safe, undermining support for a government unable to provide security.

Five Health Ministry officials, including three doctors, abducted by gunmen in southern Afghanistan on Sunday were freed unharmed on Tuesday, a provincial police chief said.

Shim's mother cried hysterically after hearing the victim may have been her son. "Why did you kill him? Please save his life," she said through her tears.

Seoul called the killings a "heinous act" carried out on innocent Korean civilians whose government had no power to release Taliban prisoners from Afghan jails.

South Korea would hold "the perpetrators responsible," a presidential statement said.

The seizure of the Koreans came a day after the Taliban had seized two Germans and five Afghans in nearby Wardak province.

The body of one of the Germans was found with bullet wounds, but the other German and four Afghans were still being held by the Taliban who want Germany to pull troops out of Afghanistan. One of the Afghan captives managed to escape.