U.S. missiles killed more than a dozen people in northwestern Pakistan early Monday in a strike that apparently was aimed at al-Qaeda’s No. 2 leader, the charismatic and influential jihadist known as Abu Yahya al-Libi, U.S. and Pakistani officials said.

The terrorist commander’s fate remained unclear late in the day, amid a swirl of rumors inside Pakistan that the longtime deputy to Osama bin Laden had been badly wounded or perhaps killed in the strike. Libi’s death, if confirmed, would represent one of the biggest successes against al-Qaeda since bin Laden was killed by Navy SEALs 13 months ago.

“This would be a major blow to ‘core’ al-Qaeda, removing the No. 2 leader twice in less than a year,” said a senior U.S. official with access to classified reports from Pakistan, where officials from both countries were working to ascertain Libi’s fate.

The official, who spoke on the condition of anonymity to discuss U.S. counterterrorism operations, said Libi had been serving as “general manager” for al-Qaeda’s main branch, overseeing the terrorist group’s day-to-day operations in Pakistan as well as its links to affiliates around the world.

U.S. and Pakistani officials confirmed that missiles struck a house in North Waziristan, a tribal province on Pakistan’s border with Afghanistan, around sunrise Monday, and that multiple deaths had been reported. A security official from the area said in a phone interview that numerous “foreigners” were described as being among the victims. The term is generally used by local residents to refer to al-Qaeda fighters.

“It is unclear whether al-Libi or other high-value targets were among the dead,” the official said. He cited a “large number” of victims, including men thought to be of Arab or Central Asian descent.

A local tribal source reached by telephone also described large numbers of bodies but said civilians were being kept away from the destroyed house.

“Initially, four people were killed, but when the militants reached the spot, another strike occurred that killed many more, raising the death toll to 16,” the source said.

The Monday morning drone strike was the third since Saturday in South or North Waziristan, two tribal provinces that have served as staging grounds for Taliban and al-Qaeda attacks against the Pakistani government as well as U.S. forces in Afghanistan.

Libi, who was thought to be in his late 40s, has long been one of al-Qaeda’s most popular and influential commanders, and he had moved into the No. 2 spot after the death in August of Atiyah abd al-Rahman, a Libyan national who was killed in a missile strike in North Waziristan. Libi managed the group’s day-to-day affairs as deputy to al-Qaeda’s senior commander, Ayman al-Zawahiri.

A former member of the Libyan Islamic Fighting Group, Libi rose to celebrity within al-Qaeda’s ranks after he escaped in 2005 from the U.S. detention facility at Bagram, Afghanistan.

“The escape gave him street cred,” said Jarret Brachman, a government consultant and researcher of terrorist factions. “He also possessed a combination of charisma, religious credentials and a populist approach” that he regularly displayed in video messages broadcast on al-Qaeda-linked Web sites.

Libi’s death would be doubly unsettling to al-Qaeda’s surviving leadership because it would reveal again the extent to which Western intelligence has penetrated the organization, said Seth Jones, a Rand Corp. analyst and author of “Hunting in the Shadows: The Pursuit of al Qa’ida after 9/11.”

“They are targeting the whole range of senior leaders,” Jones said.

Khan reported from Peshawar, Pakistan. Staff researcher Julie Tate contributed to this report.