Zawahri, Bin Laden's lieutenant and the brains behind much of al Qa'eda's strategy, promised this month to press ahead with al Qa'eda's campaign against the United States and its allies.
Ayman al Zawahri appointed al Qa'eda leader
Veteran militant Ayman al Zawahri has taken command of al Qa'eda after the killing of Osama bin Laden, an Islamist website said on Thursday, a move widely expected following his long years as second-in-command.
Bin Laden's lieutenant and the brains behind much of al Qa'eda's strategy, Zawahri vowed this month to press ahead with al Qa'eda's campaign against the United States and its allies.
"The general leadership of al Qa'eda group, after the completion of consultation, announces that Sheikh Dr Ayman Zawahri, may God give him success, has assumed responsibility for command of the group," the Islamist website Ansar al Mujahideen (Followers of the Holy Warriors) said in a statement.
The bespectacled Zawahri had been seen as bin Laden's most likely successor after the man held responsible for the September 11, 2001 attacks in New York and Washington was shot dead by US commandos in Pakistan 45 days ago.
His whereabouts are unknown, although he has long been thought to be hiding along the border between Afghanistan and Pakistan. The United States is offering a $25 million (Dh92m) reward for any information leading to his capture or conviction.
The former US, intelligence officer Robert Ayers said Zawahri was "a man lacking in charisma, a pale shadow of bin Laden". "He's a grey bureaucrat, not a leader who can energise and rally the troops. The only thing his promotion will accomplish is to elevate his priority as a target for the US."
Sajjan Gohel of Asia-Pacific Foundation security consultants said Zawahri had been in practical charge of al Qa'eda for many years, but lacked bin Laden's presence and his "ability to unite the different Arab factions within the group".
Others see a more accomplished figure. London-based journalist Abdel-Bari Atwan, who interviewed bin Laden in 1996, said Zawahri was the "operational brains" behind al Qaeda and was respected in part because, he said, he had been bin Laden's chosen deputy.
"He managed to transform al Qaeda from being a small organisation focused on expelling US interests from Saudi Arabia into a global organisation. The men he brought to al Qaeda from his own Egyptian Islamic Jihad group proved to be the instruments that drove al Qaeda's international push."
Zawahri, believed to be in his late 50s, met bin Laden in the mid-1980s when both were in Pakistan to support guerrillas fighting the Soviets in Afghanistan. He was born to an upper-class Cairo family, and trained as a doctor and surgeon.