A bomb at an Islamic religious school in south-west Pakistan has killed at least six people, officials say.
Several others were injured in the blast in Qila Saifullah in Balochistan province near the Afghan border.
All casualties were students attending the madrassa, officials said. No one has admitted carrying out the attack.
Balochistan has a long border with troubled Afghanistan. Nationalist rebels in the gas-rich province are also fighting for greater autonomy.
It is not clear if the blast in Qila Saifullah, about 150km (90 miles) from the provincial capital, Quetta, was linked to the nationalist insurgency or to the conflict in Afghanistan, where the Taleban and other militants are fighting Western-backed government forces.
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Police official Mohammed Farooq told the Associated Press news agency that four students had been killed in the bombing, while two others died of their injuries later.
He said the bomb went off in a room used by an Afghan refugee, who had left after staying the night as a guest.
The bomb was concealed in clothing left by the Afghan, officials say.
"Six people were killed and five others injured, all of them students at the Imdadul Uloom seminary, when a bomb hidden in the bundle exploded during a search," provincial home secretary Furqan Bahadur told the AFP news agency.
Police say they have sealed roads in and out of the town as they search for the man.
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