The fate of three kidnapped U.N. workers in Afghanistan is unclear following their captors' announcement that they would decide Friday whether to follow through on their threats to kill them.

Afghan officials say they do not know where the hostages are being held, but are trying to locate them. 

On Thursday, the kidnappers, from a splinter Taleban group,  set the deadline for determining whether to kill them. 

The group is demanding the release of all Taleban prisoners in U.S. custody and the departure of foreign troops and U.N. personnel from Afghanistan.

The kidnappers say one of the hostages, all of whom were helping manage last month's presidential election in Afghanistan, is seriously ill because of the strain of captivity.

Some information for this report provided by AFP, AP and Reuters.