His statement did not explicitly say, however, that Al-Qaeda was behind the 7 July London bombings, which killed 52 people.
In a separate segment of the video, one of the suspected London suicide bombers, identified as Mohammad Sidique Khan, a British man of Pakistani origin, accused Western civilians of being "directly" responsible for terror attacks targeting them.
"Your democratically elected governments continuously perpetuate atrocities against my people all over the world," Khan said. "And your support of them makes you directly responsible, just as I am directly responsible for protecting and avenging my Muslim brothers and sisters."
It was not clear when the tape had been made or where.
The British government has declined to comment on the video, but a spokesman for the main opposition Conservative party said the British people would be "sickened" by the tape.