At least four people have been killed in a suspected suicide attack in north-west Pakistan, amid signs a truce with militants may be breaking down.

The blast in the town of Bannu is the first suicide attack since March when Pakistan's new government indicated it would talk with militants.

In another attack in the north-west gunmen shot dead two policemen outside a bank in the Swat valley.

Last week militants suspended talks with the authorities because of the government's reluctance to pull out troops from tribal areas.

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