KHAR: A suicide bomber blew himself up at a military checkpoint in northwest Pakistan's volatile tribal region on Saturday, killing 16 people including two soldiers, officials said.

A man wearing a vest packed with explosives walked up to the post in Khar, the main town in the restive tribal region of Bajaur, and detonated himself, senior administration official Iqbal Khattak told AFP.

"The death toll has gone up to 16 including two paramilitary soldiers," he said. Another 23 people were wounded, with six in a critical condition, he added. The injured include one security official, Khattak said.

A senior military official, speaking on condition of anonymity, confirmed the blast and military casualties.

The bomber was making his way to nearby government buildings and military barracks when he was stopped by soldiers, the official said.

Khattak later explained the soldiers were conducting a body search when the attacker blew himself up.

The checkpoint is in the town's main bazaar which was shut after the blast.

Three vehicles and four shops were destroyed in the bombing, Khattak said.

Bajaur is in Pakistan's volatile tribal belt bordering Afghanistan. The area has become a stronghold for hundreds of Islamist extremists who fled Afghanistan after a US-led invasion ousted the hardline Taliban regime in Kabul in 2001.

The suicide attack came a day after Pakistani security forces killed 24 suspected militants in air strikes and clashes on Friday in the district plagued by Taliban insurgents.

One paramilitary soldier was also killed and three wounded in Friday's clash in the town of Chinar in the district of Bajaur, which has been the site of a number of recent military offensives.

Jets and helicopter gunships have been pounding suspected militant hideouts since Tuesday, as the military steps up operations in mountainous Bajaur, the scene of a major anti-militant operation launched in August 2008.

In February 2009 the army said the area had been secured and Taliban fighters crushed but unrest swiftly flared up again and military operations have continued, part of a fresh assault on militants across the northwest.

Around 30,000 Pakistani troops backed by fighter jets and helicopter gunships went into the Taliban stronghold of South Waziristan in October, and the military says it is making progress and that militants are fleeing.

Security has has been significantly eroded over the past two-and-a-half years in Pakistan, where militant violence -- including suicide attacks blamed mostly on the Taliban -- has killed more than 2,900 people since July 2007.

Islamist fighters have vowed to avenge military operations against their northwestern strongholds.

Taliban militants shot dead two men in tribal North Waziristan after accusing them of spying for the United States, officials said.

Their bullet-riddled bodies were found dumped by the roadside in Datta Khel region, 15 kilometres (nine miles) south of the area's main town Miranshah, they said.

A note found near the bodies said the men captured last month were found guilty of spying on the Taliban, local government officials said.

The killing came as a US drone fired three missiles in North Waziristan region late Friday, killing five suspected militants.

More than 750 people have been killed in over 80 drone strikes in Pakistan since August 2008. Pakistan says drone strikes fuel anti-American sentiment in the nuclear-armed Muslim nation.

The bombings by unmanned US aircraft have soared recently, as US President Barack Obama puts Pakistan at the heart of his administration's fight against Al-Qaeda and Islamist extremists.