This picture released July 21, 2007 in Seoul via Yonhap News Agency shows South Korean Christians posing for a commemorative photograph before leaving for Afghanistan on July 13. South Korean President Roh Moo-hyun on Saturday called for the release of 23 countrymen held hostage by Taliban fighters in Afghanistan, saying they were medical volunteers.[Yonhap (SOUTH KOREA)/Reuters]

SEOUL,-- South Korea is in contact with the Taliban to secure the release of its nationals kidnapped in Afghanistan, a senior official said on July 21, as the hard-line militia purportedly shot and killed two German hostages.

South Korea "is maintaining the contact" with the militant group, who kidnapped at least 18 South Koreans, including 15 women, to try to win their freedom, South Korean Foreign Ministry spokesman Cho Hee-yong told The Associated Press.

He said more time is needed to get a clear picture of the situation but declined to give further details. A group of South Korean officials were to leave for Afghanistan later Saturday.

South Korean President Roh Moo-hyun also urged in a brief televised statement that the Taliban "send our people home quickly and safely," adding that taking civilians hostages cannot ever be justified.

Roh also spoke with his Afghanistan counterpart Hamid Karzai and asked for cooperation to quickly win the release of the South Koreans, Roh's office said.

The appeal came as the militants purportedly killed two German hostages because their government didn't submit to Taliban demands that German troops leave Afghanistan.

"The German and Afghan governments didn't meet our conditions, they didn't pull out their troops," Qari Yousuf Ahmadi, a purported Taliban spokesman, told The Associated Press by telephone from an undisclosed location.

Ahmadi offered no proof for the claim of the killings. He said the Taliban would give further information about the two bodies later.

In Berlin, a spokesman for the German government and the Foreign Ministry could not immediately confirm the reports.

The two Germans and five of their Afghan colleagues were kidnapped on Wednesday while working on a dam project in central Wardak province. A day later, militants kidnapped at least 18 South Koreans riding on a bus in Ghazni, the province to the south.

However, Ahmadi did not mention about the fate of the South Korean hostages also held by the hard-line militia. He has said the South Koreans had until noon on Saturday to withdraw their troops from Afghanistan, otherwise the South Korean hostages would be killed. On Saturday he said there had been no change in those demands.

South Korea plans to ask relevant countries to suspend search operation for the militants as it could endanger the safety of South Koreans, Yonhap news agency reported, citing an unnamed government official.

The presidential office neither confirmed nor denied the report. Repeated calls to the Foreign Ministry went unanswered.

Ahmadi warned the Afghan government and U.S. and NATO forces not to try to rescue the hostages, or they would be killed. The provincial police chief in Ghazni province said his forces were working "carefully" to not trigger any retaliatory killings.

"The enemy has threatened that there shouldn't be any kind of search operation for the Korean citizens," said Ali Shah Ahmadzai. "We have surrounded the area but are working very carefully. We don't want them to be killed."

South Korean Foreign Minister Song Min-soon said that 23 South Koreans were kidnapped and indicated that they were safe. It was not immediately clear why there was a discrepancy with the Taliban's figure of 18 kidnapped South Koreans.

Family members of kidnapped victims urged the government to accept the Taliban's demand, noting Seoul had already decided to bring home some 200 soldiers by end of this year.

"We hope that the immediate withdrawal (of troops) is made," Cha Sung-min, a relative of one of the hostages, told reporters while holding back tears.

Earlier, Song reiterated Seoul's plans to withdraw troops from Afghanistan by the end of this year as previously scheduled, hoping to appease the militants.

"The government is in preparations to implement its plan" to pull its troops out of the war-ravaged country by the end of this year, Song told reporters at a briefing.

The South Korean government informed parliament late last year that it would terminate its troop mission in Afghanistan and bring them home before the end of this year. South Korea has about 200 troops serving with the 8,000-strong U.S.-led coalition.