Taliban insurgents have kidnapped 23 Korean Christians from a bus in Afghanistan, officials said on Friday, the biggest group of foreigners seized so far in the militant campaign to oust the government and its Western backers.

The Taliban have increasingly turned to what Afghan officials call "terror tactics" -- kidnapping, suicide attacks and roadside bombs to demonstrate that the Afghan government is incapable of providing security to the people.

"Twenty-three Korean citizens, 18 women and five men, were very carelessly travelling in a chartered bus from Kabul to Kandahar yesterday, on the way to Kandahar their bus was stopped by armed men ... and they took them away," said Interior Minister spokesman Zemari Bashari.

He said the incident happened in the Qarabagh district of Ghazni province, some 175 km (110 miles) south of Kabul.

"We are still investigating which organisation they were with, and why they were travelling to Kandahar," he said.

A Korean embassy official said a search operation and also negotiations were under way with the kidnappers, who were demanding the release of Taliban prisoners held in Afghan jails.

The Taliban said they had seized 18 Koreans.

"They are safe with us, we are investigating them and our demands and reaction will be announced later," said Taliban spokesman Said Yousuf Ahmadi by telephone from an undisclosed location.

MISSIONARY FEAR

A South Korean Foreign Ministry official in Seoul said about 20 South Korean Christian volunteers were feared to have been kidnapped by Taliban insurgents.

Last year, the South Korean government tried to stop a group of 2,000 Korean Christians travelling to Afghanistan for a peace conference, fearing for their safety.

But 900 of them still came to Afghanistan, causing an uproar in the staunchly Muslim country -- where many accused them of being evangelical missionaries -- before they were all deported.

Afghanistan's ambassador to South Korea was later sacked for issuing the group with visas, a Foreign Ministry spokesman said.

South Korea has no combat troops in Afghanistan, but has a contingent of 200 engineers, doctors and medical staff.

Two Germans and six Afghans were abducted southwest of Kabul on Wednesday and are still missing.

"The German citizens are safe with us. Our demand is the withdrawal of German troops from Afghanistan and also the release of our prisoners," said Taliban spokesman Yousuf Ahmadi.

Germany said it was aware of the Taliban claim.

"We will carefully and calmly pursue developments. All necessary steps have been taken. The emergency task force is working very intensively on a quick release of both men," a German Foreign Ministry spokesman said in a statement.

One German national was kidnapped in western Afghanistan this month, but was released unharmed after a few days.

The Taliban kidnapped two French aid workers and three of their Afghan colleagues in southwestern Afghanistan in April, but later released them unharmed.