A bomb ripped through a congested market near the Afghanistan border on Sunday, killing at least 20 people and wounding 40 others, witnesses said.
Local officials confirmed at least 14 deaths in the explosion in Parachinar, administrative headquarters of Pakistan's Kurram tribal agency, about 200 miles west of the city of Peshawar. They said the toll could rise.
Amjad Ali Khan, a senior police official, said a bomb was planted in a secondhand market where people were shopping for winter clothes.
The bomb contained approximately 80 pounds of explosives, authorities said.
Officials declared a state of emergency in the area. The injured were being treated at a government-run hospital in Parachinar, with the most serious cases due to be transferred to Peshawar.
Wajid Hussain, who suffered minor injuries, said he was buying clothes in the market when the bomb exploded. Volunteers later lined up in front of the blood bank in the main hospital to donate blood, another witness said.
The explosion occurred a day after the Pakistani army said it had "broken" the backbone of Islamist militants in the country's tribal region after a more than year-long military offensive based in the north Waziristan tribal area, south of Kurram.
Army spokesman Lt. Gen. Asim Bajwa said the operation was nearly complete and that 3,400 members of various militant groups had been killed. As well, he said, 837 hideouts were destroyed. Nearly 500 Pakistani soldiers were killed in the operation.
The offensive is credited with reducing militant violence in parts of northwest Pakistan, although analysts say many extremist leaders remain in hiding or have slipped across the border into Afghanistan.