The United States vowed to destroy the new al-Qaeda leader.

"As we did both seek to capture and kill – and succeed in killing – bin Laden, we certainly will do the same thing with Zawahiri," Chairman of the U.S. Joint Chiefs of Staff Admiral Mike Mullen was quoted as saying by The Telegraph.

U.S. Defense Secretary Robert Gates also scorned Zawahiri and said he ‘lacks the charisma’ of Osama.

“First of all I think we should be mindful that this announcement by al-Qaeda reminds us that despite having suffered a huge loss ... al-Qaeda seeks to perpetuate itself, seeks to find replacements for those who have been killed, and remains committed to the agenda that bin Laden put before them,” Gates said at his valedictory press briefing at the Pentagon.

"Bin Laden has been the leader of al-Qaeda essentially since its inception," he said. "In that particular context he had a peculiar charisma that I think Zawahiri does not have. I think he was much more operationally engaged than we have the sense Zawahiri has been,” said Gates.

Zawahiri, who was a long time deputy of Osama, has already vowed to carry forward the jihad against the United States and Israel. Al-Zawahri, who is now 59, was only second to bin Laden in the terror outfit. Laden was killed in a covert operation by the CIA and U.S. Navy Seals on May 2 in a safehouse in Pakistan's Abbottabad.