Pakistani helicopter gunships and war planes hit Taliban positions in the militants' Swat valley bastion today but a curfew prevented civilians from fleeing the fighting.
The struggle in the northwestern valley 130 km from Islamabad has become a test of Pakistan's resolve to fight a growing Taliban insurgency that has alarmed the United States and other Western countries.
The military said up to 55 militants were killed in the day's clashes and four soldiers were wounded. The figures could not be independently confirmed.
Pakistan's army went on a full-scale offensive after the government ordered troops to flush out militants from the Islamist stronghold, a former tourism centre.
Fighting had already picked up earlier in the week, triggering a civilian exodus from the battle zones in recent days but concerns are growing about the fate of those still trapped and unable to move because of a curfew.
"We are feeling so helpless, we want to go but can't as there is a curfew," said one resident of Mingora, Swat's main town. "We tried to leave yesterday after authorities relaxed the curfew for a few hours, but couldn't as the main road leading out of Mingora was literally jammed with the flood of fleeing people," he said as gunship fir
boomed in the background.
Helicopters and warplanes targeted militant hideouts in Mingora and other areas in Swat, military officials said. Militants fired rockets at an army base in Mingora.
Swat administrator, Khushal Khan, said the curfew would remain in force throughout the day.
The UN refugee agency has said a "massive displacement" is underway. Citing provincial government estimates, it said yesterday up to 200,000 people had left their homes over recent days with a further 300,000 on the move or about to move.
They join 555,000 people displaced from other areas because of fighting since August, the agency said.
Many of the displaced stay with relatives or friends or find shelter on their own, but aid agencies and officials fear if the situation is protracted they will join tens of thousands in camps, further straining resources.
Pakistan Prime Minister Yusuf Raza Gilani told a news conference the government would seek international help for the displaced people.
He also said the military would do its best to avoid hurting civilians.
"This is not a normal war. This is a guerrilla war. But it is our resolve, it is the resolve of the army that there should be minimum collateral damage."
Pakistan's fight against militants sheltering near the border with Afghanistan is seen as vital to efforts to defeat the insurgency in that country.
While Swat is not next to the border, analysts say it could also become a base for Afghanistan insurgents as well as for efforts to destabilise nuclear-armed Pakistan's government.
Up to 15,000 troops have been pitched against between 4,000 to 5,000 battle-hardened militants in the valley.