RAWALPINDI, Pakistan- Pakistani forces backed by fighter jets and helicopter gunships began an offensive on Tuesday against Taliban fighters in a key valley 100 km (60 miles) northwest of the capital, Islamabad.

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.

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.

MILITANT HOTBED

Malakand is in the North West Frontier Province, a rugged and mountanious 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, but 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.

The 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 dispelled suggestions the country was in danger of falling into the hands of Taliban, saying security forces had halted operations against the militants to give politicians the chance to negotiate a settlement.

Pakistan Afghanistan