(Updates with background and Korean hostages)

KABUL, July 21 (Reuters) - Afghanistan's Taliban movement threatened to kill two German hostages if its demands were not met by 07:30 GMT on Saturday, a spokesman for the militant group said.

The Taliban are demanding release of all of the Islamic movement's members in Afghan prisons and the withdrawal of German troops from Afghanistan.

The two Germans along with six Afghans were abducted from their vehicle southwest of Kabul on Wednesday.

"The Taliban leadership council has set 12:00 (local time) as deadline for the two German hostages. And if the deadline is not met, we will kill them," said spokesman Qari Mohammad Yousuf.

He said the eight hostages were in good condition.

The Taliban leadership council will also decide on Saturday the fate of a group of Korean Christians seized on Thursday in southwest Ghazni province, the spokesman said by phone from an undisclosed location.

Authorities in Ghazni on Saturday said Afghan and foreign troops had stepped up search for the 23 Koreans which include 18 women. The Taliban say they have seized 18 Koreans.

The Afghan government said it was not aware of the Taliban ultimatum on the German hostages and German officials could not be contacted immediately for comment.

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