LONDON --A day before the first anniversary of the London bombings, Al-Jazeera television aired a video yesterday purporting to show one of the attackers warning, "What you have witnessed now is only the beginning."
The broadcast included Ayman al-Zawahiri, the No. 2 commander of al-Qaida, suggesting that al-Qaida was seeking credit for, or at least to be associated with, Britain's worst peacetime atrocity.
The bomber, Shehzad Tanweer, 22, appeared in a red-and-white-checkered headdress against a backdrop similar to a setting used in a video last September by Mohammad Siddique Khan, the suspected ringleader of the attacks. In it Khan, 30, declared: "We are at war and I am a soldier."
The four bombers killed themselves and 52 others in attacks on three London subway trains and a bus on July 7, 2005. The attacks stunned Britons in part because they were planned and carried out largely by British-born Muslims drawn to Islamic extremism.
A parliamentary report in May said that both Khan and Tanweer had visited Pakistan before the attacks, where they might have contacted al-Qaida figures or trained in the use of explosives.
It also said both men had been observed by British counterterrorism police on the "peripheries" of another terrorist operation in this country. But, it said, counterterrorism agencies failed to grasp the "development of the homegrown threat and the radicalization of British citizens."
Speaking in the accent of his native Yorkshire, in the video Tanweer said: "What you have witnessed now is only the beginning of a string of attacks that will continue and become stronger until you pull your forces out of Afghanistan and Iraq and until you stop your financial and military support to America and Israel."
Tanweer also said Britons deserved the attacks because they voted for a government that "continues to oppress our mothers, children, brothers and sisters in Palestine, Afghanistan, Iraq and Chechnya."
British police did not directly confirm the tape's authenticity.