The school on the outskirts of the Peshawar was empty when the explosion took place, police officer Hamdullah Khan said.

Officers believe a timed explosive device caused the blast, which badly damaged the building, he said.

Islamist militants in Pakistan and neighboring Afghanistan have often targeted girls' schools because they believe that women should not be educated.

Al-Qaida and Taliban militants hold sway across much of Pakistan's border regions with Afghanistan.

The army has claimed successes against the insurgents in at least three parts of the region over the last year, but the militants remain strong across much the mountainous, lawless zone.
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