Islamabad  - A suicide bomber struck a police training camp in Pakistan's restive Swat valley on Sunday, killing at least four recruits, officials said.

The attack took place in Swat's main town of Mingora, located some 140 kilometres northwest of the capital city Islamabad.

The bomber on foot penetrated the training grounds and detonated himself among dozens of trainees during a recess, a duty officer at the local police station said.

"According to initial reports, four people have been killed and several wounded," the officer said.

Police feared the casualty count could increase as many of the injured were in a critical condition.

Private television channels put the death toll as high as 15.

Mian Iftikhar Hussain, information minister in Pakistan's North West Frontier Province where Swat is located, told the private Geo News television channel that his sources said at least 12 police recruits were killed in the blast.

Pakistani security forces launched a major offensive in Swat early May, when Taliban militants refused to disarm even after a peace deal with the government and expanded their influence to nearby districts. dpa