Pakistan ? American forces launched a raid inside Pakistan on Wednesday, a senior U.S. military official said, in the first known U.S. ground assault in Pakistan against a suspected Taliban haven. The government condemned the attack, saying it killed at least 15 people.

The American official, speaking on condition of anonymity because of the sensitivity of cross-border operations, said the raid occurred on Pakistani soil about one mile from the Afghan border. The official didn’t provide any other details.

Pakistan’s Foreign Ministry protested, saying U.S.-led troops flew in from Afghanistan for the attack on a village in the country’s wild tribal belt. A Pakistan army spokesman warned that the apparent escalation from recent foreign missile strikes on militant targets along the Afghan border would further anger Pakistanis and undercut cooperation in the war against terrorist groups.

The boldness of the thrust fed speculation about the intended target. But it was unclear whether any extremist leader was killed or captured in the operation, which occurred in one of the militant strongholds dotting a frontier region considered a likely hiding place for Osama bin Laden and al-Qaida’s No. 2 leader, Ayman al-Zawahri.

U.S. military and civilian officials declined to respond directly to Pakistan’s complaints. But one official, a South Asia expert who agreed to discuss the situation only if not quoted by name, suggested the target of any raid like that reported Wednesday would have to be extremely important to risk an almost assured “big backlash” from Pakistan.