MINGORA, Pakistan - Pakistani forces have killed 143 militants over the past 24 hours in fighting in the Islamist bastion of Swat northwest of the capital, the military said on Friday.

The struggle in the scenic northwestern valley 130 km (80 miles) from Islamabad and a former center for tourism has become a test of Pakistan's resolve to fight a growing Taliban insurgency that has alarmed the United States.

Prime Minister Yusuf Raza Gilani on Thursday ordered the army to strike at militants and terrorists he said were trying to hold the country hostage at gunpoint.

Approximately 143 militants have been reported killed in Swat valley, military spokesman Major-General Atthar Abbas told a news briefing at army headquarters in Rawalpindi.

There was no independent confirmation of the toll.

On the directive of the government, the army is now engaged in a full-scale operation to eliminate the militants, he said. They are on the run and trying to block exodus of civilians from the area, Abbas said, while warning that the operation was difficult and declining to give a timeline for clearing the valley.

Earlier, military officials had said helicopter gunships, fighters and troops were all involved in Swat operations on Friday, against roughly 4,000 to 5,000 militants.

Abbas said up to 15,000 security force members were involved.

Pakistan President Asif Ali Zardari, in talks in Washington this week, assured U.S. President Barack Obama of Islamabad's commitment to defeating al Qaeda and its allies.

Pakistan efforts against militants sheltering near the border with Afghanistan are seen as vital to efforts to defeat the insurgency in that country, while increased problems with militants in areas closer to Islamabad, such as Swat, raised concern about the stability of nuclear-armed Pakistan.

CIVILIANS FLEE

Aid groups have warned of an intensifying humanitarian crisis because of the fighting. The U.N. refugee agency said a massive displacement was underway. Citing provincial government estimates, it said up to 200,000 people had left their homes over recent days with another 300,000 on the move or about to move.

They are joining another 555,000 people displaced in other areas because of fighting since August, it said.

Despite such problems, the view of at least some Pakistanis toward fighting the militants seemed to be shifting. In the past many were opposed to action, saying Washington wanted Islamabad to be a proxy in what was essentially a U.S. battle.

Now an increasing number of Pakistanis view the militants as a threat to the country, although if the military is too cavalier about use of tactics and heavy weapons that cause civilian casualties that could change. The growing refugee burden could also sour sentiment.

But at the moment some are cheering on the government.

If the government is serious in eliminating militants from Swat then we will support the military operation, Khalid Khan, a social worker and resident of the Dheri Baba area in Swat, told Reuters.

We are ready to make every sacrifice if the government really means business this time, said Gul Omer, a poultry trader, referring to previous, inconclusive military action that was followed by the peace deal.

Gilani said the government would not bow before terrorists and would force them to lay down their arms. Reinforcements have been arriving in Swat as a peace pact collapsed and fighting has intensified since Wednesday.

Authorities agreed in February to a Taliban demand for Islamic sharia law in the valley but the militants refused to disarm, and pushed out of Swat closer to the capital.

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