CAIRO, Egypt — Al Qaeda’s no. 2 embraced the London suicide bombings yesterday, warned Britain that more destruction lies ahead and promised tens of thousands of American casualties in Iraq in a brazen assertion of the terror group’s global reach.

Ayman al-Zawahri 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 the tape, parts of which were broadcast by Al-Jazeera, Mr. al-Zawahri made no direct claim that Al Qaeda carried out the July 7 attacks in the British capital, but sought instead to blame the carnage on Prime Minister 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,” Mr. al-Zawahri said.

President Bush dismissed Mr. 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, Mr. Blair’s Downing Street office declined to comment.

A terrorism analyst for Jane’s Defense Weekly, Jeremy Bennie, said Mr. al-Zawahri appeared to be trying to put an Al Qaeda stamp on the July 7 attacks on the London transit system. The bombings killed 56 people, including four attackers.

“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,” Mr. Bennie said by telephone.

Yesterday marked the seventh time Mr. al-Zawahri has used videotapes or audiotapes to speak for Al Qaeda since the September 11, 2001, attacks in America. The latest appearance followed the Egyptian physician’s pattern of issuing threats of further death and destruction if America and its allies in Iraq and Afghanistan refuse to withdraw troops from the region, including Saudi Arabia.

Mr. al-Zawahri issued the fresh threats with a Kalashnikov rifle propped against a woven cloth background. He wore a white robe and black turban and emphatically wagged his finger while speaking.

The black turban — a change from the white turban he has worn in past videos — is “a sign that it’s time of war,” said Montasser el-Zayat, an Egyptian attorney who defends Islamic radicals and who spent three years in prison with Mr. al-Zawahri. The prophet Mohammed and his followers wore black turbans during their invasions in the Arabian Peninsula, he said.

“What you have seen in New York and Washington, you Americans, and the losses you see in Afghanistan and Iraq — despite all the media blackout — are merely the losses from the initial clashes,” he said.

“If you go on with the same policy of aggression against Muslims, you will see, God willing, what will make you forget the horrible things in Vietnam,” he said. He declared that the Bush administration was repeating in Iraq the “same lies” of Presidents Johnson and Nixon in Vietnam, that they were “defending freedom.”

“There is no exit from Iraq except in immediate withdrawal. Any delay in taking that decision means nothing but more dead, more losses,” he said. “If you don’t leave today, certainly you will leave tomorrow, but after tens of thousands of dead and double the number of disabled and wounded.”

Mr. Bennie said Mr. al-Zawahri may have been using the video as a vehicle for reissuing an offer of a truce. “This seems to say you have another chance to pull out and you won’t be hit again,” the analyst said, declaring the statement coercive and not credible.

Taahir Hoorzook, of the press relations department at Al-Jazeera, said the broadcaster received the new tape yesterday. “It was left at one of our offices, and we got it from there,” he said, declining to name the location of the office.

The tape is about five minutes long and Al-Jazeera aired only 10% of it, he said. “The content of the rest of the tape, which we didn’t air, is the usual rhetoric, speaking about the Islamic lands occupied and stuff like that which we found not newsworthy,” Mr. Hoorzook said.