The US has dismissed Ayman al-Zawahiri, the new al-Qaeda chief as a pale imitation of Osama bin Laden and warned the Egyptian to expect a similar fate to his slain predecessor.
US officials painted the 59-year-old long-time number two as an "armchair general" with no combat experience, saying he not only lacked charisma and leadership skills but was also a divisive figure who could fracture al-Qaeda.
Admiral Mike Mullen, chairman of the Joint Chiefs of Staff, told al-Zawahiri to expect the same treatment meted out to bin Laden, who was killed by US commandos in the dead of night in a May 2 raid on his hideout in Pakistan.
"As we did both seek to capture and kill - and succeed in killing - Bin Laden, we certainly will do the same thing with al-Zawahiri," Mullen said.
Al-Qaeda under the new leadership of al-Zawahiri will pursue its fight against the US and Israel, the group said in a statement posted online on Thursday.
"We seek with the aid of God to call for the religion of truth and incite our nation to fight ... by carrying out jihad against the apostate invaders ... with their head being crusader America and its servant Israel, and whoever supports them," it said.
'Continuation of threat'
Robert Gates, the defence secretary, giving his valedictory press briefing at the Pentagon, could barely disguise his scorn, but warned that the announcement should serve as a reminder of the continuing al-Qaeda threat.
"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."
But Gates, who joked that it was "probably tough to count votes when you're in a cave", said al-Zawahiri faced "some challenges".
"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 al-Zawahiri has been."
Gates also alluded to possible suspicion within al-Qaeda because of al-Zawahiri's Egyptian nationality, a point taken up earlier by a senior administration official.
Al-Zawahiri had been al-Qaeda's number two for years.
Now Washington's most wanted man, al-Zawahiri was jailed for three years in Egypt for militancy and was implicated in the assassination of Egyptian president Anwar Sadat in 1981, and a 1997 massacre of tourists in Luxor.
Facing a death sentence, al-Zawahiri left Egypt in the mid-1980s initially for Saudi Arabia, but soon headed for Pakistan's northwestern city of Peshawar where the resistance to the Soviet occupation of Afghanistan was based, and then to Afghanistan, where he joined forces with Bin Laden.
His whereabouts are unknown but he is widely believed to be hiding along the border between Afghanistan and Pakistan. The United States is offering a $25m reward for any information leading to his capture or conviction.
"Only a few weeks ago when the US Secretary of State Hillary Clinton was here in Pakistan she reportedly gave Pakistan what's been described as a hitlist", Al Jazeera's Imtiaz Tyab, reporting from Islamabad, said.
"It listed five names and al-Zawahiri's name was on the list. Whether that means the new al-Qaeda leader is here we don't know for sure, but it certainly raises some questions."
Believed to be in his late 50s, al-Zawahiri met bin Laden in the mid-1980s when both were in Pakistan to support fighters battling the Soviet Union in Afghanistan.
Continuing the struggle
Al-Zawahiri vowed earlier this month to press ahead with al-Qaeda's campaign against the US and its allies, in what appeared to be his first public response to bin Laden's death.
"The Sheikh [bin Laden] has departed, may God have mercy on him, to his God as a martyr, and we must continue on his path of jihad to expel the invaders from the land of Muslims and to purify it from injustice," he said in a video message posted online.
"Today, and thanks be to God, America is not facing an individual or a group ... but a rebelling nation which has awoken from its sleep in a jihadist renaissance challenging it wherever it is."
In Thursday's statement, al-Qaeda voiced its "support [to] the uprisings of our oppressed Muslim people against the corrupt and tyrant leaders who have made our nation suffer in Egypt, Tunisia, Libya Yemen, Syria and Morocco."
The group urged those involved in the uprisings to continue their "struggle until the fall of all corrupt regimes that the West has forced onto our countries".
But Al Jazeera's Ayman Mohyeldin, reporting from Cairo, where a popular uprising toppled longtime President Hosni Mubarak in February, said the so-called "Arab Spring" had undermined al-Qaeda in many Arab countries.
"This has been a significant blow to the ideology of al-Qaeda", he said. "Many believe al-Qaeda has lost a great deal of momentum and support across the Arab world because these revolutions were able to deliver change without the use of violence."