Pakistani forces were in a tense standoff on Wednesday with hundreds of militants holding about 250 people hostage on a train they had hijacked.

The separatist Baloch Liberation Army, which has long waged an insurgency against Islamabad, has claimed responsibility for the hijacking.

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,