Associated Press A British Royal Marine Commando patrols while on duty in eastern Afghanistan, Wednesday. The Marines have joined the search for Taliban and al-Qaida fugitives in eastern Afghanistan, marking the combat debut for an elite force trained to operate in small units in mountains that rise above 10,000 feet.

WASHINGTON ÷ U.S. government personnel are searching for al-Qaida fighters in the rough tribal regions of Pakistan, which has agreed to let American troops go after militants in the South Asian country, four well-placed U.S. officials said yesterday.

The covert operation will extend the U.S. conflict against Osama bin Ladenâs terror operation in Afghanistan across the border to Pakistan as President Pervez Musharraf validates his support for the Bush administration.

ãWe have a shared concern with the Pakistanis,äone of the officials told The Associated Press. But asked about reports the military operation has begun, the official said, ãI canât say weâve gotten to that point yet.ä

The tribal areas, just over the border from al-Qaidaâs Afghan strongholds in Paktia and Paktika provinces, are historical rally points for fighters fleeing Afghanistan, former officials familiar with the region said.

U.S. officials have said al-Qaida and Taliban fighters are believed to be regrouping in the tribal areas.

The administration and Pakistan worked out rules of engagement for the military several weeks ago. This established terms for the operation, and the Musharraf government has stood by them despite reports of wavering, a second U.S. official said.

A third U.S. official, also speaking on condition of anonymity, described as premature a newspaper account that U.S. military units had participated in attacks on suspected al-Qaida hide-outs in Pakistan.

Also, the official said, American soldiers had not been wounded, as The Washington Post reported yesterday.

A fourth official said U.S. forces in Afghanistan had chased al-Qaida fighters across the border sporadically over the past few weeks, but that was separate from the covert operation.

Aziz Ahmad Khan, spokesman for the Pakistani Foreign Ministry, yesterday denied reports that U.S. personnel were present in Pakistani tribal areas searching for al-Qaida fighters.

However, Pakistani intelligence and Interior Ministry officials, speaking on condition of anonymity, confirmed that civilian U.S. agents, with the help of Pakistani authorities, are quietly doing some work in the areas to trace the remnants of al-Qaida.

Late in March, joint Pakistani-U.S. raids led to the capture of suspected terrorist and bin Laden lieutenant Abu Zubaydah, relying on American intelligence and FBI officials rather than the U.S. military.

One U.S. official said Pakistan was reluctant to acknowledge contacts with the United States about joint military cooperation in tracking down terrorists out of concern for public opinion.

He noted that Pakistani authorities themselves traditionally have been reluctant to engage in law enforcement activities in the area, preferring to leave policing to local tribal authorities.

Covert U.S. soldiers are searching for pockets of militants along the border region, the Post said.

U.S. troops based on the Afghanistan side of the mountainous frontier have been attacked several times a week over the last month and have been in several fire fights with al-Qaida militants, the Post said, citing unidentified U.S. military officials.