Tens of thousands of civilians, many on foot or donkey-led carts, took advantage of a lifted curfew to flee Pakistan's embattled Swat Valley, while the army said it had killed 400 to 500 militants in its battle against the Taliban.

The hemorrhaging of residents Sunday from a scenic valley that once attracted hordes of tourists threatened to greatly exacerbate an existing internal refugee crisis for a nuclear-armed nation already facing economic, political and other woes.

The army offensive has garnered praise from the U.S., which wants Pakistan to root out havens on its soil where Taliban militants can plan attacks on American and NATO forces across the border in Afghanistan. In an interview aired Sunday, Pakistan's president urged international support for the fight and insisted the army had enough troops in the northwest to handle the threat.

As they left Swat's main town of Mingora, some residents cursed the situation and condemned the Taliban, while others blamed Pakistani leaders for bowing to the West. "Show our picture to your master America and get money from him," some taunted.

The desperate Swat residents were trying to leave any way they could — on motorbikes, animal-pulled carts, rickshaws or foot. A ban on civilian vehicles entering the valley complicated the exodus for those without cars. Some chided an Associated Press reporter for slowing them down by asking questions.

"We are going out only with our clothes and a few things to eat on the long journey," said Rehmat Alam, a 40-year-old medical technician walking out of Mingora with 18 other relatives. "We just got out relying on God because there is no one else to help us."

Fighter jets and helicopter gunships have pounded Swat and surrounding districts over the past few days after Taliban fighters in the valley moved out and tried to impose their reign in other areas, including a stretch just 60 miles from the capital, Islamabad.

The army's nine-hour suspension of the curfew Sunday could signal a more intense operation now that more civilians have left. Army spokesman Maj. Gen. Athar Abbas said 400 to 500 militants had been killed since the operation's launch last week.

Much of the latest fighting occurred along the periphery of Swat and Shangla, a neighboring district, he said, and at least 140 bodies of alleged militants were discovered at a militant training camp in that area.

Reports that militants from Swat had filtered into Shangla came out well before the latest operation, but it also was possible that more insurgents were headed to that district to escape the bombardments in the valley.

In Swat, Mingora was relatively calm, though an army statement said 50 to 60 militants died Sunday in various parts of the valley. Taliban fighters remained visible in Mingora.

Two soldiers also died in the latest fighting, the army said. The death tolls could not be confirmed independently, and some of the army's figures could not immediately be reconciled.

In the northwest district of Mardan, government official Khalid Umerzai said Sunday that an additional 100,000 displaced Pakistanis were expected, on top of 252,000 already there.

"Vehicles loaded with people are coming down bumper-to-bumper from Swat, and we are expecting a huge crowd of people and organizing two more relief camps in Mardan and Takhtbai," Umerzai said.

Before the latest operation, some 550,000 people were registered as displaced from past offensives in other parts of Pakistan's northwest, including the semi-autonomous tribal belt, according to the United Nations.

The international aid agency World Vision said its relief workers were finding "intolerable" conditions at some camps due to soaring temperatures, overcrowding, inadequate toilets and a lack of electricity.

Many in the northwest have little faith in the weak civilian government's ability to help them, a challenge to Pakistan's leaders because disillusioned refugees could prove fertile recruiting ground for the Taliban. Prime Minister Yousuf Raza Gilani has directed millions of dollars to help the residents of the region.

In his interview with NBC's "Meet the Press," Pakistani President Asif Ali Zardari brushed aside concerns that Pakistan's armed forces are still too focused on a potential threat from longtime rival India. He said the resources devoted to the fight against the Taliban — 135,000 troops in the northwest, he estimated — were "sufficient."

"It's a war of our existence," Zardari said.

Pakistan launched the full-scale offensive Thursday to halt the spread of Taliban, who began moving into districts neighboring Swat despite a much-criticized peace deal in which Pakistani agreed to impose Islamic law in the valley and surrounding areas.

Swat lies near the Afghan border as well as the wild Pakistani tribal areas, where al-Qaida and the Taliban have strongholds and where U.S. officials believe Al Qaeda chief Osama bin Laden may be hiding.

The army says 12,000 to 15,000 troops in Swat face 4,000 to 5,000 militants, including small numbers of foreigners and hardened fighters from the South Waziristan tribal region. The army has given no details of civilian casualties, though witnesses have reported scores, apparently for fear of a public outcry that could hamper support for the offensive.