Six civilians died in a roadside bomb attack in north-western Pakistan, the army said, as it pursued its campaign of airstrikes against militants in the country's tribal regions.

Militants blew up a school minibus with a remote-control bomb in the Salarzai area of Bajaur, one of seven tribal districts in the north-west.

"Six civilians, including three lady teachers, two children and one passerby" were killed, a military spokesman said.

Nobody immediately took responsibility, but Taliban militants have struck schools in the region before.

Bajaur borders Afghanistan's Kunar province where Taliban chief Maulana Fazlullah is allegedly hiding and sending militants to attack security forces and civilians over the border.

In Khyber and North Waziristan, two other tribal districts, jets destroyed five militant hideouts, the army said. "Eighteen terrorists were killed," it said.

Pakistan in June launched an operation against the Taliban in the North Waziristan tribal region. According to the army, more than 600 rebels have been killed.