Pakistani officials say a car bomb exploded at a crowded market Friday in the northwestern city of Peshawar, killing at least six people and wounding more than 70 others.
The blast occurred outside a movie theater in the busy Khyber Bazaar, damaging the theater and nearby buildings.
Pakistani Information Minister Iftikhar Hussain told reporters the attack could be a reaction to the military's ongoing operation in the Malakhand region that includes Swat Valley.
Pakistani military officials say 17 militants and three soldiers were killed Friday, as security forces gained further control over Taliban-held areas in the region.
Officials say the month-long operation has killed more than 1,000 militants and more than 50 soldiers, and displaced nearly two million people.
A United Nations appeal issued Friday called for an additional $454 million in humanitarian aid to help civilians fleeing the conflict in the northwest.
In a statement, acting U.N. humanitarian coordinator Martin Mogwanja said the last 3 1/2 weeks have seen "the highest rate of movement" of people the U.N. has seen "for more than 20 years, anywhere in the world." He said it is also the largest displacement in Pakistan's history.
U.N. Secretary-General Ban Ki-moon said the aid was critical to the "normalization" of the thousands displaced.
Pakistan's allies on Thursday already pledged $224 million in aid for the victims of the unrest. It is not clear how much overlap there will be between the U.N. appeal and the existing donor pledges.
Pakistani troops launched the operation in the Swat Valley after militants violated a peace deal and advanced to within 100 kilometers of the capital.
In a separate development Friday, Pakistani troops fired artillery at militant targets in the northwestern tribal region of South Waziristan. The operation was said to be focused on militants loyal to Pakistani Taliban leader Baitullah Mehsud.
Some information for this report was provided by AFP, AP and Reuters.