Al-Qaeda and its new leader Ayman al-Zawahiri are reported to have released a new hit list of targets.
American media say the list, including names and photos of US officials and business leaders, has appeared on an al-Qaeda-linked website.
Washington says news that Zawahiri has taken over command of the group is a reminder that it remains a threat.
Defence Secretary Robert Gates said: “This announcement by al Qaeda reminds us that despite having suffered a huge loss with the killing of bin Laden and a number of others, 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.”
Admiral Mike Mullen, the Chairman of the Joint Chiefs of Staff, said: “He and his organisation still threaten us and as we did both seek to capture and kill – and succeed in killing bin Laden – we certainly will do the same with Zawahiri.”
Washington says it was no surprise to hear that Zawahiri had taken over commaned of al-Qaeda, given that he’d already been considered to be bin Laden’s right hand man.