U.S. officials acknowledge they know relatively little about the remote and arid Pakistani border region, have no capacity to strike there, and have few windows into the turbulent mix of Pashtun tribal and religious politics that has turned the area into a sanctuary for the Taliban leaders, who are known collectively as the Quetta Shura.

Pakistani officials, in turn, have been accused of allowing the Taliban movement to regroup in the Quetta area, viewing it as a strategic asset rather than a domestic threat, while the army has been heavily focused on curbing violent Islamist extremists in the northwest border region hundreds of miles away.

As a result, Pakistani and foreign analysts here said, Quetta, the capital of Baluchistan province, has suddenly emerged as an urgent but elusive new target as Washington grapples with the Taliban’s rapidly spreading arc of influence and terror across Afghanistan…

“Quetta is absolutely crucial to the Taliban today,” said Ahmed Rashid, a Pakistani expert on the Taliban, in a telephone interview. “From there they get recruits, fuel and fertilizer for explosives, weapons, and food. Suicide bombers are trained on that side. They have support from the mosques and madrassas.”