Just weeks after crowing victory over Osama bin Laden's al-Qa'ida forces in Afghanistan, the Bush administration is now singing a very different tune, indicating that the organisation is still very much up and running and warning of possible new attacks on US targets around the world.

The alarm was raised most clearly this week with the release of videotapes recovered from the house of Mohammed Atef, al-Qa'ida's top military commander killed in an air strike in November. The tapes, each an hour-long speech to camera by an al-Qa'ida member, were described by the Attorney General, John Ashcroft, as "martyrdom messages from suicide terrorists".

Four of the five men were previously unknown to the US authorities, including one who remains unnamed. The fifth, however, was not only known but was also deeply implicated in the 11 September attacks. Ramsi bin al-Shibh, a 29-year-old Yemeni, lived in Hamburg with Mohamed Atta, the 11 September ringleader, and is believed to have been selected as the "20th hijacker" – the missing fifth man on board United Airlines Flight 93, which crashed in the Pennsylvania countryside after an in-flight assault by the passengers.

He tried repeatedly to obtain a visa to enter the United States, but was turned down. According to an indictment handed down in US federal court last month, his place was taken by Zacarias Moussaoui, a Frenchman of Moroccan origin who was arrested in Minnesota in August after raising suspicions at a local flight school and so also failed to participate in the attacks.

Mr bin al-Shibh has been wanted in Germany since shortly after 11 September. The video not only supplies the first public glimpse of his face, but it also suggests he went to Afghanistan either immediately before or immediately after the attacks.

The videos form part of an increasingly pessimistic tone emanating from Washington. Weeks after military and political leaders said they had throttled al-Qa'ida's ability to operate, one intelligence source said this week that the organisation's core structure had remained unaffected by the war and continued to function.