The Associated Press reported Saturday that Mullah Najibullah, a Taliban official in the southeast Afghan border town of Spinboldak, had confirmed the death, but said he refused to identify the location of the airstrike. 

He said bin Laden was alive, but that seven other al Qaeda members -- who he refused to name -- died with Atef, AP reported. 

U.S. Defense Secretary Donald Rumsfeld said he could not confirm Atef's death, but added "the reports I've received seem authoritative." Rumsfeld said the information he has received indicates Atef was killed by an airstrike, rather than ground combat. 

Atef -- whose daughter is married to one of bin Laden's sons -- has been among the top three in al Qaeda since 1996, according to U.S. officials. He is considered al Qaeda's military chief and bin Laden's likely successor. The other man in the top three, Ayman al Zawahiri, is considered the brains of the terrorist operation. 

The officials did not say when the attack happened

U.S. Navy Rear Adm. John Stufflebeem, speaking at a Pentagon press briefing, said reports of Atef's death first appeared in intelligence reports based on discussions picked up after the airstrike, which he said occurred "a couple of days ago." 

He declined to give more specifics on the intelligence reports but said if true, Atef's death would be important to the U.S. war on terrorism. 

"I would just remind us once again that that's our primary missions, that's our primary focus, is getting at al Qaeda. So getting at principle leadership of al Qaeda is a positive thing," Stufflebeem said. 

One of the FBI's most wanted terrorists
If Atef was killed in an airstrike, he was probably with other al Qaeda personnel as well, meaning the airstrike had a larger impact on the terrorist network, said retired Gen. Wesley Clark, a CNN military analyst and the former supreme commander of NATO forces in Europe. 

"In military organizations, sometimes it's not just the number one or two person, but it's the supporting staff that have all the details on how to make the contacts and to how to make the plans work, and so we've probably made a very significant impact here," Clark said. 

Atef is on the FBI's most-wanted terrorist list for the killings of U.S. nationals and conspiracy to murder U.S. nationals outside the United States, and for an attack on a federal facility resulting in death, according to the FBI's Web site. The site says Atef is "alleged to be Osama bin Laden's second in command." 

A $5 million reward was offered by the FBI for information leading to his capture. 

He has been indicted for his alleged involvement with the 1998 U.S. embassy bombings in Tanzania and Kenya, the FBI states. 

An Egyptian, Atef is believed to be responsible for supervising the training of operatives. Federal prosecutors said he provided military training and assistance in 1993 to Somali tribes who violently opposed the United Nations' intervention in Somalia's civil unrest. In an October 1993 firefight, 18 U.S. Army Rangers were killed by Somali gunmen. 

Prosecutors said Atef moved from Sudan to Afghanistan with bin Laden in 1996 and served as a member of al Qaeda's leadership committee, known as the "shura," or consultation, council. 

Atef nicknamed 'the big guy'
Atef's birthdate is unknown. He held an Egyptian passport and may have once been a policeman there. More than 6 feet tall, Atef is nicknamed "Al Khabir," which means "the big guy." 

Sometime in the 1980s, Atef apparently traveled from Egypt to Afghanistan, where he met bin Laden, who was in the country fighting against the Soviet occupation. 

Jamal al-Fadl, the government's main informant on al Qaeda, testified recently at the trial of four men charged in the Africa embassy bombings that Atef was one of the founding members of al Qaeda. Atef became military commander of al Qaeda after the previous commander drowned in a ferry accident on Lake Victoria in Africa. 

Atef was at bin Laden's side during a 1998 press conference in which bin Laden announced a "fatwah," or religious ruling, against the United States. But the most recent sign of Atef's importance to bin Laden and al Qaeda was in January when Atef's daughter married one of bin Laden's sons in a ceremony held in Kandahar. 

"There are few bin Laden can trust, in terms of family, just to reinforce loyalty, it creates intricate web that can insulate any defections," said Magnus Ranstorp, the deputy director of the Center for the Study of Terrorism and Political Violence at the University of St Andrews in Scotland. 

-- CNN National Correspondent Mike Boettcher and CNN National Security Correspondent David Ensor contributed to this report.