Going by that chronology, the photograph the military presented - showing a young man with a sparse mustache and a trimmed goatee - appeared to be at least several years old.

Caldwell said the US Defense Intelligence Agency provided the picture, adding: "Everything we had was classified just 24 hours ago associated with this gentleman - this terrorist."

Yet Islamist watchers in Egypt and abroad said they had never heard of al-Masri - whose name means "the Egyptian" - and expressed skepticism about US claims that he was poised to become Iraq's new terror leader.

"His codename doesn't ring a bell for me; he's not one of the wanted Jihadis in Egypt," said Egyptian lawyer Montasser el-Zayat, who was imprisoned with al-Qaida No. 2 al-Zawahri from 1981-84.

In an indication of the confusion surrounding the identity of the group's new leader, the U.S. first announced al-Masri's name shortly after the Jordanian-born al-Zarqawi was killed June 7. But al-Qaida in Iraq later identified its new leader as al-Muhajer.

The new leader issued a Web statement Tuesday vowing to avenge al-Zarqawi's death and threatening horrific attacks "in the coming days."

"Don't be overcome with joy about killing our sheik Abu Musab (al-Zarqawi), God bless his soul, because he has left lions behind him," the statement said.

Citing recently declassified information, Caldwell said the military believes al-Masri first went to Afghanistan in 1999 to receive training and lecture on Islam to other militants. There he became an expert in building roadside bombs, skills he used in Fallujah and Baghdad.

He trained with al-Zarqawi at the al-Farouq camp in Afghanistan and they began to collaborate in Iraq. Raids in April and May in southern Baghdad recovered material confirming his high-level involvement in moving foreign fighters from Syria to Iraq, Caldwell said.

However, Yasser al-Sirri, an Egyptian who runs the Islamic Observation Center in London, said information supplied by al-Qaida in announcing the new leader pointed to another man: Abdullah bin Rashid al-Baghdadi, the leader of the Mujahedeen Shura Council - five allied groups in the Sunni Arab-dominated insurgency.

"I'm 95 percent sure that this al-Masri doesn't exist," al-Sirri said, adding that the group could be trying to cover up the nationality of its new leader to promote a broader Islamic identity.

"Al-Qaida does not want to show that he is an Iraqi because they work under the Islamic banner ... and they seek international jihad," al-Sirri said.

Caldwell acknowledged that al-Masri's ability to exert leadership over al-Qaida cells remained unclear and said other "al-Qaida senior leadership members and Sunni terrorists" could try to take over the operations.

He pointed to al-Baghdadi along with Abu Abdul-Rahman al-Iraqi, whom al-Qaida in Iraq statements have identified as the group's deputy. Al-Iraqi was believed to have been killed in the airstrike along with al-Zarqawi.

Mustafa Alani, a terror expert at the Gulf Research Center, said the ultimate call for the new leader would be made by bin Laden or al-Zawahri, believed to be hiding in the rugged border area between Pakistan and Afghanistan.