North Waziristan, which borders Afghanistan, is a sanctuary for al-Qaeda and Taliban fighters and has been the scene of fierce battles and suicide attacks over the past several years.

Unpopular campaign

A large number of Arab and Central Asian fighters linked to al-Qaeda are reported to be hiding near the town of Mir Ali, the site of Saturday's attack, officials said.

Pakistan's new government has committed itself to the US-led campaign against the fighters even though the campaign is unpopular throughout the country.

A senior official in the administration of George Bush, the US president, said on Friday Pakistan was not equipped to combat the fighters.

"This is a problem that's been created in sovereign Pakistani territory and the problem is going to be solved when Pakistan has an ability to exercise control over that territory," said Stephen Hadley, Bush's national security adviser.

"We recognise that in the short term right now there are threats emanating out of that area that threaten Pakistan, that threaten our troops in Afghanistan and potentially threaten the homeland," he said, referring to the US.

Madrassa blast

An explosion at an Islamic school, known as a madrassa, near the Pakistani city of Quetta on Friday, killed five students and wounded eleven others, Pakistani police said.

"The madrassa people say that someone threw explosives into it, but we are investigating," Wazir Khan Nasir, a police official, said.

"We are looking into all possibilities including ... whether they were preparing some explosives," another official said.

Quetta is the capital of Baluchistan, a southwestern province bordering Afghanistan, where a large number of madrassas were set up in the 1980s to raise volunteers to fight against the Soviet occupation of Afghanistan in a war covertly funded by the United States and Saudi Arabia.

The Taliban came from the Baluchistan madrassas.

But Baluchistan is also fiercely independent inside Pakistan and ethnic Baluch fighters are also battling Pakistani security forces for more autonomy for their region.