He said the two top Western allies risked losing thousands of lives if they did not pull out of Iraq or end the Israeli occupation of Palestinian and Muslim lands.

"These policies (of British Prime Minister Tony Blair) will bring them more destruction after the explosions of London," Zawahiri said.

His statement came as thousands of police mounted a huge operation to protect London, exactly four weeks after suicide bombers brought carnage to the city, killing 52 people.

Zawahiri, who in the footage appeared to be standing outside with an assault rifle at his side, also warned the Americans of horrors worse than the war in Vietnam.

"The Americans... will see horror that would make them forget the horror they saw in Vietnam," he said.

"You people of the crusade alliance, we proposed (asking) you to at least refrain from harming Muslims. The lion of Islam, Osama bin Laden, also offered you a truce to leave the lands of Islam," he said.

"Did he (bin Laden) not tell you that you will not dream of security before we live in Palestine and before you withdraw (your) infidel troops" from Muslim land, he asked.