The US has vowed it will kill newly appointed Al Qaeda leader Ayman Al-Zawahiri in a similar raid that led to the death of Osama Bin Laden on May 1.

"He (Zawahiri) and his organisation still threaten us. As we did both seek to capture and kill and succeed in killing bin Laden, we certainly do or will do the same thing with Zawahiri," Admiral Mike Mullen, Chairman of the US Joint Chiefs of Staff, told reporters at a Pentagon news conference late on Thursday.

Robert Gates, US Secretary of Defense, speaking at his last press conference while still in office, stated he doubted whether Zawahiri would turn out as successful as his predecessor, as he lacked Bin Laden's charisma.

" I think he was much more operationally engaged than we have the sense Zawahiri has been," he added.

On Thursday, it was announced that Ayman Al-Zawahiri has been elected to succeed Osama bin Laden as head of the Al Qaeda terrorist organization.

Al-Zawahiri was the person most analysts expected to be announced as bin Laden's successor, since he has been his deputy for more than a decade.

The decision to appoint Al-Zawahiri was made to pay respect to the "righteous martyrs" and to honor the legacy of bin Laden, CNN reports, citing jihadist websites.

"Hereby the General Command of the Qaida al-Jihad - and after the end of the consultations -- we declare that Sheikh Dr. Abu Muhammad Ayman Al-Zawahiri (May God bless him) will take over the responsibility of command of the group," the cited statement says.

Osama bin Laden was hunted down in a US assassination raid on May 1 2011 and subsequently buried at sea.

Ten days after the assassination, former Bulgarian police executives revealed that the Bulgarian authorities failed twice to arrest Al-Zawahiri in 1995 because of legal and security reasons.