PESHAWAR, Pakistan - A suicide bomber attacked a gathering of displaced people waiting to get aid in northwestern Pakistan on Saturday, killing at least 40 of them, a hospital official said.

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The attack in the Bajaur region on the Afghan border came a day after a big clash between Pakistani Taliban insurgents and security forces in the neighbouring Mohmand region that left 11 soldiers and 24 militants dead.

"I myself have counted 40 bodies but the death toll could rise as several wounded people are in critical condition," Dosti Rehman, an official at the main government hospital in Bajaur, told Reuters.

A government official in Bajaur, Wisal Ahmed, said the people gathering to get food rations had been forced from their homes by earlier fighting between the security forces and the al Qaeda-linked militants.

Pakistan's volatile ethnic Pashtun tribal lands on the Afghan border have been infested with militants and the army has mounted a series of operations to dislodge them.

Hundreds of militants have been killed and many of their strongholds have been captured but the insurgents have shown the ability to strike back and have killed hundreds of people in a campaign of bomb attacks across the country.

A senior military official in October said it would take at least six months to clear militants from Bajaur and Mohmand.