Qari Yousef Ahmadi, who claims to speak for the Taliban, said the militants had pushed back the deadline until Tuesday evening after the Afghan government refused to release any of the 23 Taliban prisoners the insurgents want freed.

The developments came as the US-led coalition reported killing some 50 militants in southern Afghanistan's poppy-growing heartland.

A woman, a family member of one of the kidnapped South Koreans in Afghanistan, cries as she waits for television news about them in Seoul at around 1300 GMT July 23, 2007. [Reuters]

The kidnappers have extended their ultimatum at least three times. Afghan officials in Ghazni province have met the militants in person and are also negotiating over the phone, but little progress appears to have been made so far.

"If the government won't accept these conditions, then it's difficult for the Taliban to provide security for these hostages, to provide health facilities and food," Ahmadi told The Associated Press by satellite phone. "The Taliban won't have any option but to kill the hostages."

Though some of Ahmadi's statements turn out to be true, he has also made repeated false claims, calling into question the reliability of his information.

Deputy Interior Minister Abdul Khaliq, meanwhile, said Afghanistan was not prepared to make a deal "against our national interest and our constitution," though he did not explicitly rule out freeing any prisoners.

President Hamid Karzai in March authorized the release of five Taliban prisoners in exchange for a kidnapped Italian reporter, but he called the trade a one-time deal. Karzai was also criticized by the United States and European nations who felt that trade would encourage more kidnappings.

Khail Mohammad Husseini, a lawmaker from Ghazni province, where the Koreans are being held, said a delegation of provincial leaders tried to meet with the kidnappers Monday but that the militants didn't show.

He said officials were also speaking with the militants by telephone, and that the insurgents at one point had increased their demands, saying all jailed militants in Ghazni province had to be released. But Ahmadi denied that the demands had changed, suggesting the Taliban weren't presenting a unified front.

Meanwhile, Ahmadi also said the militants are still holding one German and four Afghan hostages, despite the fact Ahmadi on Saturday claimed those six people had been shot and killed.

He said the Taliban were demanding the release of 10 Taliban prisoners in exchange for the German and Afghans. Originally there had been five Afghan hostages, but one of them, the brother of Afghanistan's Parliament speaker Arif Noorzai, "escaped" from Taliban custody, Ahmadi said.

Francesc Vendrell, the EU representative for Afghanistan, said officials are not convinced the Taliban is actually holding the German and the Afghans. Police have suggested that the five might be held by a separate criminal group.

The body of the second German, Ruediger Diedrich, 43, was to be flown back to Germany on Monday, where authorities will carry out an autopsy, the German Foreign Ministry said. His body was discovered riddled with bullet holes, but officials haven't concluded if he first died of another cause and was later shot.

The South Korean hostages were kidnapped Thursday while riding on a bus through Ghazni province on the Kabul to Kandahar highway, Afghanistan's main thoroughfare.

The Afghan military has the region surrounded in case the government decides the military should move in.

South Korea has banned its citizens from traveling to Afghanistan in the wake of the kidnappings, said Han Hye-jin, a Foreign Ministry official. He said Seoul also asked Kabul not to issue visas to South Koreans and block their entry into the country.

South Korea had previously asked its nationals to refrain from visiting Afghanistan, citing political instability.

Earlier, the South Korean church that the abductees attend said it will suspend at least some of its volunteer work in Afghanistan. It also stressed that the Koreans abducted were not involved in any Christian missionary work, saying they only provided medical and other volunteer aid to distressed people in the war-ravaged country.

Neither the Afghan nor Korean governments have commented on the purported Taliban trade offer. A delegation of eight Korean officials arrived in the capital of Kabul on Sunday and met with Karzai to discuss the crisis.

The 23 South Koreans, including 18 women, were working at an aid organization in Kandahar, said Sidney Serena, a political affairs officer at the South Korean Embassy in Kabul.

South Korea has about 200 troops serving with the 8,000-strong US-led coalition in Afghanistan, largely working on humanitarian projects. They are scheduled to leave Afghanistan at the end of 2007.

In the two-day battle in the Sangin district in Helmand province, the insurgents tried to shoot down a coalition aircraft and attack soldiers with a suicide car bomb, the coalition said. Coalition aircraft dropped four bombs and Afghan forces counted "more than four dozen" insurgents killed, it said.

The Sangin district chief, Eizatullah Khan, said a large group of Taliban had attacked a convoy Sunday, and the resulting battle left more than 30 militants dead and many wounded.

Coalition and Afghan forces "only engaged legitimate military and enemy targets to minimize the potential of Afghan casualties," said US Maj. Chris Belcher, a coalition spokesman. "We did this even as the insurgents tried to create some propaganda value by placing innocent civilians in harms way."

Civilian casualties have been a major problem for US and NATO forces this year. Taliban militants often fight in populated areas or seek cover in civilian homes, leading to the deaths of ordinary Afghans.

Officials reported a Norwegian coalition soldier was shot and killed while on operation in central Afghanistan.

In Zabul province, Afghan police forces reported killing 14 "enemies" during a 12-hour battle Sunday, including a Taliban commander identified as Mohammad Hassan.

Afghan elders leading the hostage negotiations met with the kidnappers Sunday and reported that the Koreans were healthy, said Khwaja Mohammad Sidiqi, a local police chief in Ghazni district. The Koreans were kidnapped there Thursday while riding on a bus from Kabul to Kandahar on Afghanistan's major highway.

The Afghan military has the region surrounded in case the government decides the military should move in.