WASHINGTON, May 31, 2010 (AFP) - The death of Mustafa Abu al-Yazid would be "a big victory... a major blow to Al-Qaeda," because as the group's number-three figure "he had a hand in everything," a US official said Monday.
Al-Qaeda announced the death of its top leader in Afghanistan and trusted aid to Osama bin Laden, as reported by the US-based SITE group, which monitors Islamist websites.

"We have strong reason to believe that's true, and that (Yazid) was killed recently in Pakistan's tribal areas," said the US official, who asked to remain anonymous.
"In terms of counterterrorism, this would be a big victory."
The SITE statement did not say how Yazid died, but Al-Qaeda sent a message to jihadist forums saying his wife, three of his daughters, his granddaughter, and other men, women, and children, were killed.
Yazid, an Egyptian national also known as Sheikh Said, was said to be a founder member of Al-Qaeda and a former treasurer to bin Laden.
The US official said Yazid was "widely viewed" as Al-Qaeda's number three leader.
Yazid "was the group's chief operating officer, with a hand in everything from finances to operational planning. He was also the organization's prime conduit to Bin Laden and (second-in-command, Ayman) Zawahiri.
"He was key to al-Qaeda's command and control.
"His death would be a major blow to al-Qaeda, which in December lost both its internal and external operations chiefs," the official added.
He took Yazid's demise as "further proof that the tribal areas (in Pakistan) are not quite the safe haven al-Qaeda and its allies thought them to be.
An expert with intelligence analysis firm IntelCenter said Yazid ran Al-Qaeda's operation in Pakistan and Afghanistan.
His death, the analyst added, "is one of the most significant blows against al-Qaeda in recent years and its impact will be felt by the group."
Yazid, said to be a former member of the Egyptian Jihad, has appeared in a number of videos released by Al-Qaeda since he first appeared as head of Al-Qaeda in Afghanistan in May 2007.
His last public statement was in a message released on May 4, SITE said.