The separatist Baloch Liberation Army claimed responsibility for attacking the train carrying 440 passengers in a tunnel in a remote part of Balochistan. Spokesman Jeeyand Baloch had said the group was ready to free passengers if authorities agree to release jailed militants.

ISLAMABAD — Pakistan’s neglected southwestern province of Balochistan has been the scene of a yearslong insurgency, with a dramatic uptick in attacks in recent years underscoring the struggles the government in Islamabad faces in dealing with myriad security threats.