Pakistan's military ordered people out of parts of the Swat valley on Sunday, temporarily relaxing a curfew to enable civilians to flee an intensifying offensive against Taliban militants.

Pakistan hopes to stop a growing Taliban insurgency with its offensive in the former tourist valley 130 km (80 miles) from Islamabad after US criticism that the government was failing to act against the Islamist militants.

Almost 200 militants have been killed in the fighting in recent days, according to the military. The figure could not be independently confirmed.

Hundreds of thousands of people have left Swat in the past week and in all about 500,000 are expected to get out. They join 555,000 people displaced earlier from Swat and other areas  because of fighting since August.

"We have ordered the civilian population in four districts to vacate the areas," said Nasir Khan, a military spokesman in the region. "They have seven hours to leave because we have to strike militant hideouts there."    

The army went on a full-scale offensive on Thursday after the government ordered troops to flush out militants from the Taliban stronghold.

The offensive was launched while President Asif Ali Zardari, the widower of former prime minister Benazir Bhutto, was in Washington assuring a nervous United States his government was committed to fighting militancy.

Most political parties and many members of the public support the offensive, although that could change if the displaced are seen to be suffering unduly or if many civilians are killed.

Fighting had intensified two days before the offensive was launched, triggering a civilian exodus as a February peace pact collapsed, but concern has been growing for those trapped and unable to move because of the curfew.

The exodus resumed with the lifting of the curfew for seven hours on Sunday although residents said transport was scarce because the military was not letting vehicles into the valley.

"Everybody wants to get out of this hell," Zubair Khan, a resident of Mingora, the valley's main town, said by telephone.

"Some are driving out while many are just on foot. They don't know where they're heading but staying here just means death."  Helicopters and warplanes targeted militant hideouts in Mingora and other areas in Swat on Sunday, the military's Nasir Khan said, adding he had no information about casualties.

"It's a tough battle. They're operating in small groups. They don't fight a pitched battle but we're closing in on them, squeezing them and have cut their supply lines," he said.

Vehicles had been stopped coming in to the valley because the military feared the militants might try to send in reinforcements, the military spokesman said.

Vehicle operators were demanding ever higher fares, residents said. "How can I take my kids, wife and old mother to a safer place? Nobody thinks of humanity, money is their religion," said teacher Mohammad Shahnawaz said.

Many displaced stay with relatives or friends or in rented accommodation but aid groups fear those numbers will join the tens of thousands in camps if the crisis is protracted.

The World Vision aid group said high temperatures, insufficient toilets and a lack of electricity made conditions in camps "intolerable" despite the efforts of the authorities and aid agencies.

"We may not be able to meet the most basic needs of the refugees as quickly as they are arriving in the camps if it continues at this pace," Jeff Hall, a deputy director for World Vision, said in a statement.

Separately, security forces killed 24 Taliban insurgents in a clash in the Mohmand region on the Afghan border on Saturday night after militants attacked a paramilitary camp, a paramilitary force official said. - Reuters