"I suspect the number of dead might go up as many of the wounded are in critical condition," Fazl-e-Rabi, a police official, told the Reuters news agency.

The bomber was apparently making his way to nearby government buildings and military barracks when he was stopped by soldiers.

The checkpoint is in the town's main bazaar, three vehicles and four shops were destroyed in the bombing, Khattak said.

Air attacks

The suicide attack came a day after Pakistani security forces killed 24 suspected fighters in air attacks and clashes in the town of Chinar, also in the district of Bajaur.

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One paramilitary soldier was killed and three others wounded in the clashes.

Also on Friday a suspected US drone fired three missiles in North Waziristan killing at least nine people.

Missiles hit a compound alleged to be used by Taliban fighters in the town of Muhammad Khel.

The identities of those killed in the attack were not immediately known.

The targeted compound was said to be a centre for local Taliban and was also a base for fighters belonging to the Haqqani network, which is known for staging attacks on US and Nato troops in Afghanistan.

Previous raids

A series of drone raids have been carried out this month in North Waziristan, home to fighters loyal to the Taliban, al-Qaeda and the Haqqani network.

A number of US raids in early January are reported to have targeted Hakimullah Mehsud, the leader of the Pakistani Taliban.

He was initially reported dead, but an audio recording purportedly carrying a message from Mehsud dispelled rumours of his death and vowed revenge for the drone programme.

The US never confirms drone attacks, but its forces in neighbouring Afghanistan and the Central Intelligence Agency are the only ones known to use the unmanned aircraft capable of firing missiles.

The attacks have often resulted in civilian deaths, stirring anger among Pakistanis and even bolstering support for the Taliban and anti-US sentiment.

More than 750 people have been killed in over 80 drone attacks in Pakistan since August 2008.