Thousands of Pakistanis skirted burning military trucks Thursday as they fled clashes between Taliban militants and the army in the northwest, adding a humanitarian emergency to the nation's daunting challenges.

Refugees overwhelmed camps and hospitals to the south of the fighting, leading Pakistan's prime minister to make a late-night appeal Thursday for international assistance. The International Committee of the Red Cross said fighting had cut access to places where civilians were most in need.

The U.S. has praised the gathering military operation in the Swat Valley and neighboring districts where Taliban guerrillas had extended their reach to within 60 miles of the Pakistani capital, Islamabad. Pakistan's president, in Washington for meetings with the Obama administration, insists they can turn back a tide of rising militancy also threatening neighboring Afghanistan.

But with some 45,000 people fleeing, the pro-Western government faces a stiff task to keep an already skeptical nation behind its security forces as they respond to U.S. pressure to uproot radicals. The exodus adds to the more than 500,000 already displaced by fighting in Pakistan's volatile border region with Afghanistan.

On Thursday, several thousand men, women and children — some on foot — took advantage of an easing in the army curfew to pour through Swat's main town, Mingora, in search of safety.

Convoys of colorful trucks, cars and buses, most overflowing with people and their belongings, traveled hours over mountainous terrain to reach camps in and around the city of Mardan some 40 miles away.

At the Tuberculosis Hospital in Mardan, hundreds jostled before overwhelmed volunteers to register for a tent and a handout of emergency supplies.

Yar Mohammad, a 50-year-old stone mason, said he had "poured his blood" and his best years into the development of Swat. "And now I am seeing the buildings that I have helped to construct being blown up and destroyed," he said, blaming both the Taliban and the authorities.

Some residents complained that the Taliban had blocked their escape.

Ayaz Khan said he loaded his family into his car Thursday in the Kanju area of Swat only to find rocks, boulders and tree trunks laid across the roads, forcing him to turn back.

"I am helpless, frustrated and worried for my family," he said.

Military operations are taking place in three districts that stretch over some 400 square miles, but most of the fighting has been in the main town of Mingora, which before the insurgency three years ago was home to around 360,000 people.

The military claimed to have killed more than 80 militants in Swat and the neighboring Buner region on Wednesday. Officials have said nothing about civilian casualties. But those fleeing the region bore tales of families wiped out by stray shells.

Fazl Hadi, a doctor at another hospital in Mardan, said 45 civilians had been admitted with serious gunshot or shrapnel wounds in recent days and was bracing for many more.

Among the youngest patients was Chaman Ara, a 12-year-old girl with shrapnel wedged in her left leg. She said she was wounded last week when a mortar shell hit the truck taking her family and others out of Buner.

She said seven people died, including one of her cousins, and pointed to a nearby bed where the boy's wounded mother lay prone. "We mustn't tell her yet. Please don't tell her," she whispered.

A spokeswoman for the U.N. refugee agency, said the world body has registered more than 45,000 refugees in recent days. They join more than 500,000 already driven out by fighting in other regions of the northwest over the past year who are already living with relatives or in camps.

"We are in an emergency phase," U.N. spokeswoman Ariane Rummery said. The refugee problem is "becoming much larger, and much more serious."

In Mingora, witnesses said armed militants were again roaming the streets Thursday, and that troops were launching artillery and airstrikes on Taliban targets in the area.

An AP Television News cameraman saw four burnt out and abandoned army trucks, two of them still smoldering, on the road leading out of Mingora.

Gen. Ashfaz Parvez Kayani, the chief of Pakistan's army, said it would commit enough of its resources to "ensure a decisive ascendancy over the militants" in the country.

Kayani did not say whether the army intended to add to the some 15,000 troops already in the valley, but a U.S. military official said Americans were "noticing movement. There is a reorientation of some forces going on toward the northwest from the east." The official did not give his name because he was not authorized to speak to the media.

Washington has said it wants to see a sustained operation in Swat and surrounding districts, mindful of earlier, inconclusive offensives elsewhere in the Afghan border region. Eight years after the Sept. 11, 2001, attacks, the area remains a haven for Al Qaeda and Taliban fighters blamed for spiraling violence in Pakistan and Afghanistan.

The Swat peace accord that provided for Islamic law in the region began unraveling last month when Taliban fighters moved into Buner.

Troops were also assailing militants in the nearby Dir region. A spokesman for Sufi Muhammad, the hardline cleric who helped put together the peace deal, said Muhammad's son died in army shelling in Dir late Wednesday.

Khan accused the government of unleashing the army "to appease America and get dollars" — a common view among Pakistanis, strengthened by the coincidence of the latest fighting with Zardari's high-profile visit to Washington.