Multiple bombs exploded in two Pakistan cities on Thursday, just hours after Taliban groups warned people to evacuate several large cities, saying they were preparing "major attacks." The groups also claimed responsibility for a bloody attack in Lahore a day earlier that killed at least 26 people. Three bombs detonated in Peshawar, northwest of Pakistan’s capital, and one exploded in Dera Ismail Khan, in the country’s troubled west, killing at least 11 people and wounding dozens. The attacks were reminders of the potency of militants in Pakistan, a nuclear-armed American ally that is fighting a war against the Taliban in its north and west. Pakistan is central to American policy in this region; militants in its lawless tribal areas cross the border into Afghanistan, where the United States is fighting a similar insurgency.