By Augustine Anthony
RAWALPINDI, Pakistan (Reuters) - Pakistani forces backed by jets and helicopter gunships began an offensive on Tuesday against Taliban fighters in a valley just 100 km (60 miles) northwest of the capital, Islamabad, part of a new campaign to halt the rapid advance of the militant Islamists.
Military spokesman Major-General Athar Abbas said he expected it would take up to a week to clear an estimated 500 militants from Buner district, the latest target of an operation launched on Sunday in nearby Lower Dir.
"The aim of the offensive is to eliminate and expel militants from Buner," Abbas told a news conference in the garrison town of Rawalpindi, next door to Islamabad.
The Taliban's creeping advances across Malakand have raised alarm in Washington that militants were zeroing in on Islamabad and have stoked fears the nuclear-armed country was on the verge of sliding into chaos.
The Pentagon welcomed the Pakistani military operation and urged Islamabad to remain on the offensive.
"The key is to sustain these operations at this tempo and to keep the militants on their heels and to, ultimately, defeat them," Pentagon press secretary Geoff Morrell said.
"The test of all of these Pakistani military operations -- because we've seen them from time to time in the past -- is always their sustainability," he told reporters in Washington.
Washington is considering rushing hundreds of millions of dollars in emergency aid to Pakistan, according to the U.S. Senate's second-ranking Republican, Jon Kyl of Arizona.
"It may be appropriate, and I believe the administration is looking right now at ... somewhere between two and four hundred million dollars, for both counter-insurgency and economic assistance, that we could pass really quickly, in just a matter of days," he told reporters in Washington.
MILITANT HOTBED
Pakistan's President Asif Ali Zardari agreed this month to impose Islamic sharia law in Malakand in a vain bid to persuade the Taliban in Swat to lay down their arms.
Instead, emboldened by the government's concessions, Taliban fighters began spreading.
Malakand is in the North West Frontier Province, a rugged and mountainous area bordering Afghanistan and a hotbed of militant Taliban activity.
Abbas said 10 soldiers and up to 75 militants had been killed in the Buner fighting. Independent casualty figures were not available.
"I warn them to vacate the area. We are not going to spare them," Interior Minister Rehman Malik told reporters before the military announced the Buner offensive.
Residents of Mingora, Swat's main town, said militants had taken up positions in a bazaar there, raising fears of a showdown with security forces.
Militants also plastered posters on the walls of buildings warning journalists to be more balanced in their coverage of the Taliban.
"They should mend their ways, otherwise they will be responsible for the consequences," they warned.
London-based Amnesty International said on Tuesday that around 33,000 people were reported to have left their homes in Lower Dir over the past two days.
In Swat, meanwhile, militants kidnapped three policemen and later killed one of them.
"The dead body of one of them was found near Swat river," police chief Danishwar Khan told Reuters. "They are still holding two others."
Pakistani army chief Ashfaq Kayani last week rejected suggestions the country was in danger of falling into the hands of the Taliban, saying security forces had halted operations against the militants to give politicians the chance to negotiate a settlement.
(Additional reporting by Andrew Gray and Susan Cornwell in Washington and Junaid Khan and Zeeshan Haider in Pakistan; Editing by David Fox and Eric Walsh)
