A South Korean woman held hostage with 21 others in Afghanistan has pleaded for help to secure their release.The woman, who identified herself as Yo Syun Ju, told the BBC by telephone she was "sick and in a terrible situation". "Tell them to do something to get us released," she said in an interview carried out in the presence of the Taleban militants holding her captive. A group of 23 Koreans was abducted one week ago. The kidnappers have since killed one of the hostages.