Pakistan's military launched operations in Bajaur in August 2008 and have repeatedly claimed to have eliminated the Islamist militant threat.
The country's northwest tribal belt is a stronghold of Islamist groups, including home-grown jihadi cells as well as extremists who fled Afghanistan after the US-led invasion toppled the hardline Taliban regime at the end of 2001.
American military commanders in Afghanistan have repeatedly expressed frustration that Pakistan has not done more to rid its rugged frontier of al-Qaeda and Taliban-linked groups, such as the Haqqani Network which is able to launch attacks on international forces from their havens across the border.
Police and local administration officials confirmed the attack in Khar was carried out by a woman, according to their initial examination of the bomber's remains.
The local administration imposed an indefinite curfew in Khar, while security forces patrolled streets and launched a search operation in the area, officials said.
About 4,000 people have died in suicide and bomb attacks across Pakistan since 2007, when security forces raided an extremist mosque in Islamabad, turning terrorist networks against a regime that had previously offered tacit or at times overt support to Jihadi groups.
However, Pakistan vehemently denies accusations that it is not doing enough to eradicate the Taliban in the northwest, saying more than 2,400 troops have been killed in fighting Islamist militants from 2002 until April this year.