PESHAWAR: Pakistan said it killed more than 80 militants in an upsurge of fighting Wednesday that caused tens of thousands to flee and threatened to torpedo a northwest peace deal.

The military announced the death tolls ahead of a three-way summit between President Asif Ali Zardari, US President Barack Obama and Afghan President Hamid Karzai, after which Obama said the leaders had renewed their commitment to fight extremism.

Helicopter gunships and artillery swung into action against Taliban in Swat Wednesday in the deadliest fighting reported in the northwest former ski resort since a February deal sought to end a nearly two-year Taliban insurgency.

"Security forces were being targeted from emerald mines. In retaliatory fire 35 militants were killed," the military said in a statement.

A military official in the area said helicopter gunships and artillery bombarded the mines before ground troops recaptured the area from the Taliban. He also said there were reports of civilian casualties in fighting in Swat.

In separate clashes in nearby Buner district, at least 49 militants were killed.

Pakistan's cash-strapped government made emergency preparations to shelter up to 500,000 people who they expect to flee Swat and local officials said tens of thousands streamed out of the district's main town.

"More than 40,000 have migrated from Mingora since Tuesday afternoon," said Khushhal Khan, the chief administration officer in Swat.

Bedraggled men, exhausted women in burkas and anxious children poured off pick-up trucks and buses with tales of horror about their treatment at the hands of the Taliban, who have sought to impose sharia law, bombing girls schools and beheading officials.

"They (the Taliban) killed my husband, they slit his throat after accusing him of spying," said 40-year-old Zarina Begum, pleading for help as she staggered off a bus in Pakistan's main northwestern city, Peshawar.

"A mortar hit my house and as a result, I lost one of my eyes. Please take me to hospital, I want medical treatment," she begged.

Although a three-month peace accord appeared in tatters, spokesmen for the government and the pro-Taliban cleric who signed the deal, Sufi Mohammad, insisted before the deadly fighting was announced that it remained intact.

Mian Iftikhar Hussain, spokesman for the government in North West Frontier Province, did not confirm an exact number of displaced but said the government was building more emergency shelters.

The army branded militant attacks a "gross violation" of the peace accord and said four soldiers had been killed in fighting in Swat since Tuesday. It said two other militants, in addition to the 35, were also killed in Swat.

In signs that the fighting was spreading, Pakistani artillery pounded shells at militant positions in the mountain town of Khawazakhela, but there were no immediate reports of casualties, a local military official told AFP.

In Mingora, Taliban entered several houses and were using local residents as "human shields," the officer said on condition of anonymity.

Taliban spokesman Muslim Khan claimed his fighters controlled "more than 90 percent" of Swat, where government forces have been largely confined to their bases in the past.

"If the government launches an operation against us we will give them a fitting reply, which it will remember for a long time," Khan told AFP.

The government was heavily criticised for the February deal to put three million people in the northwest under sharia law in a bid to end the uprising, which instead saw the Taliban push further south towards the capital Islamabad.

In the Pakistani capital, army chief of staff General Ashfaq Kayani briefed Prime Minister Yousuf Raza Gilani on the security situation in the country.

Elsewhere, artillery bombarded insurgent positions in Buner, killing 27 militants and destroying eight vehicles, paramilitary forces said.

And at least 22 militants were killed in separate clashes in the district, paramilitary forces said, adding that a force was sent in after a report that 50 militants were looting villagers.

Ten days ago, Pakistan launched offensives in Buner and in Lower Dir, which neighbour Swat, to flush out advancing armed Taliban.

Pakistan is under US pressure to crush militants, which Washington calls the biggest terror threat to the West.