The remaining 21 South Korean hostages were alive on Wednesday after another Taliban deadline expired, an Afghan official said, adding the army had dropped leaflets warning of an assault to rescue them.

|PIC1|"The hostages are alive," said Khowja Seddiqi, district chief of Qarabagh, in Ghazni province, where the 23 Christian volunteers were abducted nearly two weeks ago by the Taliban.

"The national army has dropped leaflets through helicopters telling people in several districts to evacuate their houses because it wants to launch an operation," he told Reuters.

The defence ministry could not be reached immediately for comment.

Earlier the ministry said the Afghan National Army had launched an operation in Ghazni, but insisted it was "routine" and was not linked with the kidnapping.

The head of the Afghan government team tasked with trying secure the release of the hostages has not ruled out use of force to end their ordeal.

The Taliban could not be immediately be contacted. The movement has repeatedly said that any use of force would jeopardise the lives of the remaining hostages.

Earlier in the day, a Taliban spokesman said the group was expecting to hear from Afghan mediators over its demand for the government to release rebel prisoners, but insisted some of the hostages would be killed if that demand was not met by 0730 GMT.

The Afghan government has said that giving in to rebel demands would only encourage more kidnapping.

The hostages' desperate relatives, keeping an agonising vigil in Seoul, appealed to the U.S. government to intervene. South Korean lawmakers also made a joint appeal to Washington to act.

The Taliban spokesman said two women among the 21 Koreans were now seriously ill.

"The majority of the hostages are ill, but two females are seriously ill and there is this possibility that they may die," Qari Mohammad Yousuf told Reuters by telephone from an undisclosed location.

He said the pair suffered from an unknown illness and the Taliban did not have the right medicines to treat them.

NO DEAL

The Islamic movement killed two male hostages after previous deadlines expired.

Afghan officials have said no deal would be struck with the Taliban and demanded the unconditional release of the remaining captives, 18 of them women. The group of 23 had been sent by a Christian church in Seoul to do relief work in Afghanistan.

President Hamid Karzai came under sharp criticism after releasing a group of Taliban prisoners in March in return for the freedom of an Italian journalist.

South Korea is under intense pressure to bring the hostages home but concedes it has few cards to play. Seoul has called for "flexibility", a comment analysts say is directed at the United States to pressure Kabul to strike a deal with the kidnappers.

A U.S. State Department spokesman has said Washington "does not make concessions to terrorists".

The abduction of the Koreans comes after 18 months of rising violence in Afghanistan, the bloodiest period since the Taliban were ousted from power by U.S.-led and Afghan forces in 2001.

A day before seizing the Koreans, the Taliban abducted two German aid workers and five Afghan colleagues in Wardak province, which, like Ghazni, lies to the southwest of Kabul.

One German was found shot dead and one of the Afghans managed to escape. The other German and four Afghans were still being held.

The Taliban have demanded Germany pulls its 3,000 troops out of Afghanistan as the main condition for freeing the other German.

Al Jazeera aired silent footage of a man against a rocky backdrop, guarded by a militant with a rocket-propelled grenade.

"The German hostage Rudolf B. ... urged Germany and the United States to pull out their forces from Afghanistan and urged his country to help save his life and secure his return to his homeland and family," the station presenter said.

German Chancellor Angela Merkel has said Berlin would not give in to the kidnappers' demands.

Separately, the Taliban have killed four Afghan judges they kidnapped in Ghazni two weeks ago, a provincial official said on Wednesday. The bodies of the four, killed on Tuesday night, were found to the south of the town of Ghazni on Wednesday, he added.