It "barely matters" who the new leader of al-Qaeda is, US officials have said, following the appointment of Ayman al-Zawahiri to replace Osama Bin Laden. The comments, by US State Department spokeswoman Victoria Nuland, followed remarks by an unnamed US official earlier that Zawahiri had "nowhere near" Bin Laden's credentials. Zawahiri has for a long time been the militant group's second-in-command. Its leader Bin Laden was killed by US special forces in Pakistan in May. 'Lacking charisma' A statement announcing Zawahiri's appointment was posted on a militant website on Thursday and attributed to al-Qaeda's General Command. "Sheikh Dr Ayman al-Zawahiri, may God guide him, assumed responsibility as the group's amir [leader]", it said. The statement vowed that that under Zawahiri, it would pursue jihad or holy war against the US and Israel "until all invading armies leave the land of Islam". But Zawahiri's appointment was given a scornful response by the unnamed senior US official, who said he had not "demonstrated strong leadership or organisational skills" in the past. "His ascension to the top leadership spot will likely generate criticism if not alienation and dissention with al-Qaeda," the Obama administration official said, speaking on the condition of anonymity. He added that Zawahiri, 59, would find it difficult to lead while focusing on his own survival. "The bottom line is that Zawahri has nowhere near the credentials that [Osama Bin Laden] had," said the official from President Barack Obama's administration. Analysts say Egyptian-born Zawahiri is intelligent but lacks the charisma of his predecessor. He is claimed by some experts to have been the "operational brains" behind the 9/11 attacks on the US. For years Bin Laden's deputy, with a $25m (£15m) bounty on his head, he had been widely anticipated to replace Bin Laden at the helm. Zawahiri, whose 60th birthday is believed to be this Sunday, warned just over a week ago that Bin Laden would continue to "terrify" the US from beyond the grave. Divisions? The BBC's Middle East correspondent, Jon Leyne, says priorities for al-Qaeda's new leader may include attempting to mount a big attack to show the organisation is still in business. In addition, he says, Zawahiri will want to turn the wave of unrest in the Middle East to al-Qaeda's advantage - perhaps building more of a power base in Yemen and working to intensify the instability there. In his message last week, Zawahiri applauded the Arab uprisings against "corrupt and tyrant leaders" and urged those involved to continue their "struggle until the fall of all corrupt regimes that the West has forced onto our countries". But our correspondent adds that the delay in announcing Zawahiri as al-Qaeda chief - coming as it does more than six weeks after Bin Laden's death, despite his being the obvious choice - may point to divisions within the leadership. Zawahiri has for years had a bounty on his head and security analysts have suggested he is most likely to be hiding in the Afghan-Pakistan border region. However, Bin Laden and other key militant leaders who were also believed to be concealed there have instead been discovered in Pakistani towns and cities. Source: BBC