Four weeks to the day after suicide bombers killed 56 people on subway trains and a bus in London, Al-Jazeera television broadcast the tape by Ayman al-Zawahri in which he also renewed terror threats to other countries with troops in Iraq and Afghanistan, claiming they had shunned Osama bin Laden's offer last year of a truce if foreign forces left the battleground.
In London, thousands of police monitored the streets and subways. Not, officials say, in response to specific intelligence, CBS News Correspondent Richard Roth reports, but because London is still under major threat.
Al-Zawahri made no direct claim that al Qaeda carried out the July 7 attacks in the British capital, but sought instead to blame to carnage on Prime Minister Tony Blair's decision to deploy and keep troops in Iraq. Britain maintains 8,500 forces mainly in southern Iraq.
"Blair has brought to you destruction in central London, and he will bring more of that, God willing," al-Zawahri said in the tape, which was excerpted by the pan-Arab satellite channel.
CBS News Correspondent Mark Knoller reports that in Crawford, Texas, President Bush said the latest threats from al-Zawahri make it clear that Iraq is part of a war on terror. He said al Qaeda is trying to force the United States out of Iraq, but it won't succeed.
Mr. Bush dismissed al-Zawahri's threat, saying, "We will stay on the offense against these people. They're terrorists and they're killers and they will kill innocent people ... so they can impose their dark vision on the world."
In London, Blair's Downing Street office declined to comment on the tape.
Jeremy Bennie, a terrorism analyst for Jane's Defense Weekly, said al-Zawahri appeared to be trying to put an al Qaeda stamp on the London attacks.
"He has tacitly taken responsibility by claiming al Qaeda is in control of the situation, even as most people aren't really sure bin Laden and al-Zawahri still are capable of organizing such an attack," Bennie said in a telephone interview.
Thursday marked the seventh time al-Zawahri has used video- or audiotapes to speak on behalf of al Qaeda since the Sept. 11, 2001, attacks in the United States. The latest appearance followed the Egyptian-born physician's pattern of issuing threats on further death and destruction if the United States and its allies in Iraq and Afghanistan refuse to withdraw troops from the region, including Saudi Arabia — home to two of Islam's holiest shrines.
Al-Zawahri issued the fresh threats with a Kalashnikov rifle propped against a woven cloth background that moved with the wind and showed the sunlight, suggesting the scene was filmed outdoors. He was wearing a white robe and a black turban and emphatically wagged his finger at the camera while speaking.
The black turban — a distinct change from the white turban he has worn in past videos — is "a sign that its time of war," said Montasser el-Zayat, an Egyptian attorney who defends Islamic radicals and who spent three years in prison with al-Zawahri. The prophet Muhammad and his followers wore black turbans during their invasions in the Arabian Peninsula, he said.
Al-Zawahri is "exploiting the whole atmosphere following London and Sharm el-Sheik explosions to carry out the sort of instigation that propels more operations," el-Zayat said.
As the Iraqi insurgency led by bin Laden's Jordanian comrade Abu Musab al-Zarqawi continued killing Iraqis and American forces almost at will, al-Zawahri promised more savagery.