On the eve of the first anniversary of the attacks on London's transit system, one of the suicide bombers appeared posthumously on video Thursday to warn that the violence is not over.

Pointing his finger at the camera, Shehzad Tanweer warned that the July 7, 2005 attacks, which killed 52 people and injured hundreds, were only the beginning of a campaign of terror.

"What you have witnessed now is only the beginning of a series of attacks that will continue and increase in strength until you withdraw your soldiers from Afghanistan and Iraq, and until you (the British government) stop your financial and military support for America and Israel," Tanweer said in English on the video, aired Thursday by Al-Jazeera television.

Tanweer, 22, killed seven people and himself aboard a London Underground train. All four of the July 7 suicide bombers were British.

Ahmed al-Sheikh, an editor at Al-Jazeera in Doha, Qatar, would not say how or when the Arab broadcaster obtained the video. He said it was a long tape, and the station had shown only a small portion of it. The package the broadcaster received contained clips showing Al Qaida No. 2 Ayman al-Zawahri and Usama bin Laden.

The latest video showed a still picture of bin Laden. The Al Qaeda leader was paraphrased as paying tribute to Tanweer and the bombings, calling it the "crowning achievement of Al Qaeda's work."

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In September, Al-Jazeera played a video from another of the four bombers, Mohammad Sidique Khan. The background of both videos appear to be identical, suggesting both tapes may have been made in the same place. The backdrop seemed to be a kilim, or Oriental rug, hung on a wall.

In September's video, Khan claimed that the British public were to blame for the terror attacks because of their support for Western governments which "continuously perpetuate atrocities" against the Islamic world.

Khan's farewell message had been broadcast alongside a video of al-Zawahri, warning of more attacks. They did not appear together on the recording, but analysts said it provided the strongest link yet between the terrorist network and the four London bombers.

At the Tanweer family home in Beeston, West Yorkshire, 200 miles north of London, a sign had been posted in the window telling members of the media to stay away.

Irshad Hussain, a friend of the family, said the bomber's relatives would be "devastated" to see the video of Tanweer.

"It will be really, really hard for them. They are still trying to come to terms with what has happened, and to see their son on the screen will be torture," Hussain said.

British police were alerted to the existence of the tape within the past 24 hours, a police official said on condition of anonymity, as they are not authorized to publicly discuss the investigation.

Andy Hayman, head of Specialist Operations for the Metropolitan Police, said the video would become part of the continuing investigation of the bombings.

"There can be no doubt that the release of the video at this time can only cause maximum hurt and distress to the families and friends of those who died on 7/7 and the hundreds of people who were injured in the terrorist attacks," Hayman said.

Prime Minister Tony Blair's official spokesman said Blair intended to make no comment on the video or its content.

"We want the attention to focus on the quiet reflection of the nation as a whole tomorrow, we don't think anything should be able to get in the way of that," said the spokesman, who speaks only on condition of anonymity as he is a nonpolitical civil servant.

The airing of the video on Thursday, the day before the first anniversary of the attacks, was timed for maximum impact, experts said.

"Somebody is trying to put the frighteners on us, and it's a horrific way to treat the British public," said Anthony Glees, director of the Brunel Center for Intelligence and Security Studies at Brunel University. "It's very disturbing, but also very important in identifying that these people have been used by Al Qaeda or Al Qaeda allied organizations. That this tape has been stored for over a year, it makes the makes the point that we are under threat.

"The public will be very wary of traveling tomorrow and I think people will need to be very alert."

Nader Mozakka, whose wife Behnaz died in the attacks, said the tape was "a smack in the face."

"They have released it at the time when a lot of survivors are going through hell," he said. "This is typical of the enemy that we have. They have no respect — they kill innocent people."