The blasts hit as a convoy of police and paramilitary troops passed through the town of Matta near the hilly Swat area, well known as a stronghold of pro-Taliban militants.

The latest attack came a day after a suicide bomber killed 18 Pakistani paramilitary soldiers and wounded 24 in the volatile North Waziristan tribal region on the Afghan border.

Military spokesmen said that attack in North Waziristan might have been linked to last week's commando storming of a radical mosque in the capital, Islamabad. The army said 75 people had been killed in the assault on the Lal Masjid mosque-religious school complex. Interior Minister Aftab Ahmed Sherpao said on Friday that 60-65 of the dead were militants and four or five of them were foreigners.

Nearly 50 people have been killed in bomb attacks targeting troops and police in the northwest since July 3, when security forces surrounded the mosque complex following clashes with gunmen based there.