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, AP news agency reported.
The town of Dargai, near the Swat border, is reported to be where at least one camp is being built.
Syed Shoaib Hasan
BBC News, Islamabad
Pakistan's security forces are now poised to storm into the Swat district in a showdown which will end any chances of peace in the near future.
This operation is being seen as pivotal in the struggle against the Taleban.
If it fails, Swat could turn into an even bigger safe haven for militants and al-Qaeda than the tribal areas.
A Pakistani military spokesman, Maj Gen Athar Abbas, told the BBC the Taleban had violated all the norms of the peace deal in Swat Valley.
He said the Taleban had sent out armed patrols and had gone into the neighbouring Dir and Buner districts.
The army says militants attacked checkpoints and bases in four different locations in Swat, and that armed militants are openly patrolling the streets of the district's main city Mingora.
A witness in Mingora told AP that black-turbaned militants were deployed on most streets and on high buildings, and that security forces were barricaded in their bases.
Khushal Khan, district co-ordination officer in Swat, told the BBC that residents of areas around Mingora had been told to evacuate because there was a fear that the Taleban could use heavy weapons to attack security forces.
But he said the order was later rescinded when the attacks no longer seemed likely.
A UN camp shelters people displaced by the fighting in the north-west region
However, reports say residents are fleeing in their hundreds anyway, taking advantage of the government's lifting of a curfew.
Taleban spokesman Muslim Khan said that the militants were in control of "90%" of the valley.
He told AP that Taleban actions were in response to the army violating the peace deal. He said the peace deal had "been dead" since the army's recent offensive in neighbouring Buner district.
"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 and Afghan President Hamid Karzai were preparing for talks in Washington on Wednesday.
Analysts say US President Barack Obama will seek assurances from Mr Zardari that his country's nuclear arsenal is safe from Taleban insurgents and that Pakistan intended to root-out militant groups and defeat them.
Following bilateral discussions, the three leaders will come together for talks in what Washington's envoy to Afghanistan and Pakistan, Richard Holbrooke, called "unprecedented trilateral co-operation".
Mr Holbrooke told the foreign affairs committee at the House of Representatives that the US must provide "unambiguous" support to a democratic Pakistan headed by Mr Zardari.
Militants fought the army in Pakistan's north-west from August 2007 until this year's deal.
Under the deal the Taleban were expected to disarm.
The Taleban say they will not lay down their arms until Islamic Sharia law is fully implemented in Swat.
They have banned the playing of music in cars and are also using mosques to invite local youth to join them.
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