Page last updated at 20:33 GMT, Thursday, 12 March 2009 The kidnappers of three foreign aid workers in Sudan's Darfur region have demanded a ransom, say officials. The Medecins Sans Frontieres staff were abducted on Wednesday along with two local staff who were later released. The kidnappings come after Sudan ordered the expulsion of 13 aid groups, including the French and Dutch chapters of MSF, e