At least nine people were killed when a roadside bomb exploded close to a prison vehicle and a school bus in north-western Pakistan, officials say.

The remote-controlled device exploded in the Upper Dir district of North-West Frontier Province near the Swat Valley.

Officials said those killed by the blast included four schoolgirls, three policemen and two of the prisoners.

Earlier, a suicide bomb attack on the main police complex in central Islamabad wounded at least 13 people.

The bombings came just over two weeks after more than 50 people were killed and more than 260 wounded in a suicide bombing at the capital’s Marriott hotel.

They also happened as parliament met in a special session for a second day for a classified security briefing on Pakistan’s internal security situation.

The joint session was called to try to help form a national consensus on how to tackle Islamic militancy and the surge in suicide bombings.

Local officials said the improvised explosive device was detonated by remote control as a vehicle carrying a group of prisoners from court to jail passed by.

A school bus which was also driving past at the time was also hit by the blast, they added.

Unconfirmed reports said at least 10 people were wounded.

Upper Dir district lies close to the Swat Valley and the border with Afghanistan, where security forces have been battling pro-Taleban militants since October last year.

Pakistani security forces said they had detained 18 suspected militants in the valley during an operation on Wednesday, local media reported. Large quantities of arms and ammunition were also seized.

Earlier, a suicide bomber partially destroyed an anti-terrorist squad building inside a police complex in Islamabad, injuring 13 people.

The inspector-general of Islamabad Police, Asghar Raza Gardezi, told the BBC the bomber had driven a green vehicle into the Police Lines complex shortly before midday and parked outside a three-storey office block.

He then got out of the car and entered the building, where he put a bag of sweets he claimed to be selling on the desk of a policeman, Mr Gardezi added.

Moments later, there was a large explosion which destroyed a corner of the building. Shoes were strewn among the rubble.

Mr. Gardezi said the authorities would be looking into why a civilian vehicle was allowed into the police compound in the first place, and how the bomber evaded security checks at the entrance.

Another police officer told the BBC that it had been fortunate that many of the officers stationed in the building had been guarding parliament and other areas of Islamabad at the time of the blast.

The attacks in Islamabad and Dir drew condemnation from the Prime Minister, Yusuf Raza Gillani, who said the perpetrators of such heinous crimes would not be spared and would be brought to justice.