Residents of Pakistan's Swat Valley are reported to be fleeing their homes despite authorities rescinding an earlier order for them to leave.

A peace deal between the government and Taleban militants in the region appears close to collapse after the army said militants attacked police checkpoints.

There has also been heavy fighting to the west and east of Swat, the BBC reported Tuesday.

In other violence, a suicide bomber killed four security personnel near Peshawar, North West Frontier Province.

Police said the attacker rammed an explosive-laden car into a military vehicle.

It is not yet known who is behind the attack, but Taleban militants are known to be active in the province.

Pakistani Information Minister Mian Iftikhar Hussain said the government was preparing six camps to cater for up to 500 000 people fleeing fighting in the region.

A Pakistani military spokesman, Maj-Gen Athar Abbas, said the Taleban had violated all the norms of the peace deal in Swat Valley.

Taleban spokesman Muslim Khan said that the militants were in control of "90%" of the valley.

"Everything will be OK once our rulers stop bowing before America," he said.

The deteriorating situation in Pakistan's north-west came as President Asif Ali Zardari was preparing for talks in Washington on Wednesday.

Analysts say US President Barack Obama will seek assurances from Zardari that his country's nuclear arsenal is safe from Taleban insurgents and that Pakistan intended to root-out militant groups and defeat them.