MARDAN, Pakistan – Army helicopters dropped Pakistani commandos behind Taliban lines in the Swat Valley on Tuesday as part of a widening offensive against the militants, while a U.S. missile killed eight people in an attack on a suspected insurgent hideout elsewhere in the northwest.

Choppers inserted troops into the remote Piochar area in the upper reaches of the valley, an army statement said. Officials identified it as the rear-base of an estimated 4,000 Taliban militants also entrenched in Swat's main towns. It is seen as possible hiding place of Swat Taliban chief Maulana Fazlullah.

A military spokesman declined to give details of the Piochar assault.

Pakistani authorities launched a full-scale assault on Swat and surrounding districts last week after the Taliban pushed out from the valley on the back of a now-defunct peace deal and extended their control to areas just 60 miles (100 kilometers) from the capital, Islamabad.

The military response has won praise from American officials, who insist Islamabad must eliminate safe havens used by militants to undermine the pro-Western governments in both Afghanistan and Pakistan. The government claims to have killed some 700 militants in Swat and neighboring districts so far.

But it has also unleashed a tide of at least 360,000 refugees. Their plight could sap public support for the kind of sustained action against an increasingly inter-linked array of Islamist extremists that the cash-strapped country's Western backers are desperate to see. Around 30,000 are staying camps set up by the government and international organizations.

Also Tuesday, a missile strike destroyed a house in Sara Khora, a village in the South Waziristan tribal region, Pakistani security officials said. The identities of those killed were not immediately known.

Two security officials, citing initial intelligence reports, said eight people died. They said agents on the ground were still trying to discover the identities of the victims. The officials asked for anonymity because they are not authorized to speak openly to the media.

Yar Mohammad, a resident of the area, told The Associated Press by telephone that he had seen Taliban militants removing nine bodies from the building and taking them away in vehicles. The discrepancy over the number of deaths could not be reconciled immediately, but was not unusual in the aftermath of such attacks.

Over the past year, the U.S. has carried out dozens of missile strikes on al-Qaida and Taliban targets in the border area, where American officials say al-Qaida chief Osama bin Laden is likely hiding.

Pakistani leaders publicly oppose the tactic, saying it fuels anti-American sentiment and makes it easier for extremists to recruit. U.S. officials say the strikes, apparently carried out by CIA drones, have killed a string of al-Qaida operatives and minimized civilian casualties.