Abu Yahya al-Libi, one of al Qaeda's top strategists and seen as the most prominent figure in the network after leader Ayman al Zawahri, may have been killed in a drone strike in northwest Pakistan, Pakistani intelligence officials said on Tuesday.
If his death is confirmed it would be the biggest blow to al Qaeda since U.S. special forces killed Osama bin Laden in a secret raid in Pakistan in May 2011.
US sources said Libi, a Libyan cleric with a degree in chemistry who has survived previous drone attacks, was a target of a strike early on Monday in the North Waziristan tribal region, home to some of the world's most notorious militant groups.
Some US officials describe Libi, whose real name is Mohamed Hassan Qaid, as number two to al Zawahri, the former Egyptian doctor who took over al Qaeda after bin Laden's death.
Pakistani intelligence officials told Reuters they believe Libi (which means Libyan in Arabic) may have been among seven foreign militants killed in Monday's strike.
One of the officials said Pakistani authorities had intercepted telephone chatter about Libi, an al Qaeda theologian and expert on new media whose escape from a US-run prison in Afghanistan in 2005 made him famous in al Qaeda circles.
"We intercepted some conversations between militants. They were talking about the death of a 'sheikh'," one of the Pakistani intelligence officials said, referring to the title given to senior religious leaders.
"They did not name this person but we have checked with our sources in the area and believe they are referring to al-Libi."
A militant commander in North Waziristan closely associated with foreign fighters however said: "He has not been killed. This is not the first time claims have been made about his death. The Americans are suffering heavy losses in Afghanistan so they have resorted to making false claims."
It can take months to confirm whether drone strikes have killed an Islamist militant leader because the area of the attack is often sealed off by the Taliban in the lawless northwest of Pakistan.
Burials are quick in order to hide casualties and identities.
If a drone strike did kill Libi, it would bolster the American argument that drones are a highly effective weapon against militants.
The Pakistan government says that, while the CIA-run pilotless drone campaign has some advantages, it fuels anti-American sentiment in the country and is counterproductive because of collateral damage.
Drones are a sticking point in current talks between the United States and Pakistan aimed at repairing ties damaged by a series of events, including the recent imprisonment of the Pakistani doctor who helped the CIA hunt down bin Laden.
According to reports from North Waziristan, which American government sources did not contest, US-operated drones launched three attacks along Pakistan's border with Afghanistan between Saturday and Monday.
Reports from Pakistan said nearly 30 people were killed during the sequence of strikes, including four suspected militants on Saturday, another 10 on Sunday, and 15 people in the strike in which Libi was targeted.
Libi, reportedly born in 1963, made repeated appearances on al Qaeda videos and wrote prolifically, becoming one of the group's most prominent media warriors.
A biographer, Jarret Brachman, says Libi was seen as having made al Qaeda "cool" for a younger generation.