Baloch separatist group claims responsibility, says it has killed six security personnel as it holds hundreds hostage.

The militants, Baloch ethnic fighters, said they would kill dozens of seized security personnel if the Pakistani government did not agree to a prisoner exchange.

Pakistani security forces are carrying out a rescue operation to free dozens of passengers taken hostage by separatist militants who hijacked their train in the southwest of the country on Tuesday. Here is a look at what happened,