Pakistan must immediately lift a curfew in the Swat Valley and airlift food, water and medicine to residents trapped by battles between the military and the Taliban or risk a humanitarian catastrophe, Human Rights Watch warned Tuesday.

Tens of thousands of civilians are thought to remain in the valley and surrounding districts, where the army faces a major test of the country's resolve to take on militants with a strong grip on parts of the country.

More than 2 million people have fled the fighting, an exodus encouraged by government forces because it moves noncombatants out of harm's way and makes insurgents easier to identify.

The outflow has reduced the threat of civilian casualties, but left more than 160,000 people in refugee camps and a dozen times that number staying with relatives or elsewhere.

Those left behind are hemmed in by the fighting in some places and unable to flee in others because the military has surrounded towns and blocked off several ways out.

"The government cannot allow the local population to remain trapped without food, clean water, and medicine as a tactic to defeat the Taliban," Brad Adams, the New York-based Human Rights Watch's director for Asia, said in a statement.

"People trapped in the Swat conflict zone face a humanitarian catastrophe unless the Pakistani military immediately lifts a curfew that has been in place continuously for the last week."

Pakistan's military said the situation was too dangerous for civilians to be allowed to move freely in the valley.

"The fighting is on there, and how do you expect the curfew be lifted?" Maj. Gen. Athar Abbas told The Associated Press.

He said the army was sending trucks with food and other supplies to areas that forces have cleared.

Militants on Monday pledged to temporarily stop attacking security forces in Mingora out of concern for trapped civilians. The promise appeared designed to appeal to growing public concern for those stuck in Mingora and could indicate they were preparing a tactical withdrawal from the city.

The U.S. has strongly backed Pakistan's month-old offensive in the northwest valley and neighboring districts. U.S. officials want Pakistan to root out havens used by Al Qaeda and Taliban fighters to plan attacks on Western troops in nearby Afghanistan, and Swat is considered an important test of the Muslim nation's ability and willingness to do so.

The army says it secured several major intersections in Mingora, a key commercial hub that under normal circumstances is home to at least 375,000 people. Many of the extremists were fleeing the city for Kabal, a town to the west that security forces were also trying to secure, the army said in a statement Monday.

The military says about 1,100 suspected insurgents have died so far in the offensive.

It has not given a civilian death toll, and it's unclear how it is separating noncombatants killed from militants. Residents fleeing the region have reported dozens of ordinary Pakistanis killed in the fight. Journalists have mostly been barred from reporting there.