The German government has called upon Yemeni tribesmen to release four German tourists taken hostage earlier this month.

The foreign ministry issued a statement saying the government is particularly mindful of the fate of the three men and a woman on this Christman holiday after twenty days in captivity.

It said they should be released immediately and without conditions.

More than one hundred foreigners have been abducted since 1992, but most have been well-treated and released unhurt.

It is belived Yemeni tribes kidnap foreigners to pressure the government into making concessios in local disputes.