The US government has said that it killed Mustafa Abu al-Yazid, an Egyptian man described as al-Qaeda's "number three" official.
Al-Qaeda confirmed al-Yazid's death in a message posted on internet forums on Monday.
The message contains no details about his death, but US officials believe al-Yazid, also known as Sheikh Sa'id al-Masri, was killed in northwest Pakistan last month.
"We have strong reason to believe ... that al-Masri was killed recently in Pakistan's tribal areas," a US counter-terrorism official told the Reuters news agency.
Al-Yazid was a longtime member of al-Qaeda and was described by a US official as being the organisations "chief operating officer".
It was unclear exactly where or how al-Yazid was killed.
Born in Egypt in 1955.
Al-Qaeda's third-in-command, behind Osama bin Laden and Ayman al Zawahiri.
Founding member of Egyptian Islamic Jihad, one of the groups that merged to form al-Qaeda.
Al-Qaeda's leader in Afghanistan, Pakistan, Uzbekistan, Tajikstan and Iran.
Served as a top propagandist for al-Qaeda and Taliban.
Former treasurer of al-Qaeda.
Pakistani news reports speculate that he was killed in a US drone strike, but US officials would not comment.
"And there's some controversy here, because nobody in Pakistan has confirmed where he was killed," Al Jazeera's Imran Khan, reporting from Lahore, said.
The US government also alleged that he helped to funnel money to some of the hijackers in the September 11, 2001 attacks in the US.
Al-Yazid headed al-Qaeda's Afghanistan branch for several years, and reportedly ran many of the group's operations in both Afghanistan and Pakistan.
"He was also the organisation's prime conduit to bin Laden and Zawahiri," the US official said, referring to al-Qaeda leader Osama bin Laden and his deputy, Ayman al-Zawahiri.
The al-Qaeda message said that al-Yazid's wife, and several other family members, were killed along with him.
Al-Yazid was a former member of Egypt's Islamic Jihad organisation and spent time in prison after Anwar Sadat, the former Egyptian president, was assassinated in 1981.
His last public statement was issued on May 4, wherein he praised Abu Omar al-Baghdadi and Abu Ayyub al-Masri, the two al-Qaeda in Iraq leaders killed in a raid in April.