We extend our deep appreciation to the Government of Pakistan... but deeply regret the deaths of those soldiers killed in the line of duty

US State Department

Officials say hundreds of reinforcements backed by helicopters have been sent to boost the operation in the remote tribal area of South Waziristan in Pakistan's North West Frontier Province.

The army has also been questioning members of the local tribe in the area where the al-Qaeda suspects are thought to have been hiding.

"Army troops are conducting house-to-house searches in villages scattered throughout the difficult hilly terrain," the Interior Ministry's Brigadier Javed Cheema told the French news agency AFP.

Tribal sources in the nearby garrison town of Wana told the BBC that four US operatives were also involved in the encounter, but this has not been confirmed.

The United States Government said it deeply regrets the soldiers' deaths.

"Since 11 September, Pakistan has time and again shown itself to be a stalwart partner in the coalition against terrorism," a State Department statement said.

"That several of its soldiers have made the ultimate sacrifice once again proves its commitment to our common struggle against terror."

Pakistan has deployed about 12,000 troops in tribal areas, traditionally outside the control of the central government, in an attempt to stop al-Qaeda and Taleban fighters slipping over the border from Afghanistan.

First engagement

Wednesday's gunfight took place in Kazha Panga village, some 30 kilometres (20 miles) from the border with the Afghan province of Paktika.

Tribal areas have their own laws

An Interior Ministry official in Islamabad said the soldiers came under heavy fire when they closed in on a suspected militant hideout.

The four-hour clash was the first time that suspected al-Qaeda fighters have engaged Pakistani forces in the region since President Pervez Musharraf ordered troops to the border in December.

Two men believed to be al-Qaeda fighters were also killed in the gunfight.

There were no further details on the US operatives involved.

But US Army Green Berets, CIA paramilitary units and telecommunication experts are all active in the area, searching for Osama bin Laden and other al-Qaeda and Taleban officials.

Casualties

Ahmad Khan, a senior Pakistan government official in Wana, said six Pakistani troops and three suspected al-Qaeda fighters were also wounded in the exchange.

Of the troops killed, six were regular Pakistani soldiers - including two officers - and four belonged to the paramilitary Frontier Corps.

Tribal areas were once a no-go zone

Pakistani officials said the two al-Qaeda fighters killed were Chechens but tribesmen in Wana said they were either Tajiks or Uzbeks.

There were also reports that one al-Qaeda fighter was captured but the Pakistani authorities have yet to confirm this.

New checkpoints have been set up in recent weeks and troop patrols intensified in an attempt to capture al-Qaeda and Taleban fighters.

Pakistan until recently resisted US pressure to launch largescale search operations in the semi-autonomous border region for fear of provoking tribal opposition.

But army officials say they have received the full co-operation of tribal leaders in North and South Waziristan, previously considered no-go areas.

The tribal areas, set up after partition from India, stretch for hundreds of miles along the border with Afghanistan.

Although strictly speaking part of Pakistan, they have their own laws and customs and the authorities' writ does not run there.