The al-Qaeda leader's first video message for three years featured a bizarre rant against America, with references to global warming, "insane taxes", the US mortgage market meltdown and rising interest rates.

	Image conscious: Osama bin Laden appears to have dyed his beard to seem younger

American spy chiefs were quick to name Adam Gadahn, the head of al-Qaeda's English language media operations, as the author of large sections of bin Laden's broadcast.

Last October, the 28-year-old "loner" became the first American charged with treason since 1952, for appearing in a succession of al-Qaeda videos under the guise of "Azzam The American", in which he condemned globalisation and made American cultural references.

He was charged in his absence, as he is thought to be near to bin Laden, almost certainly in the tribal areas of Pakistan.

The bin Laden video, timed to coincide with the sixth anniversary of the 9/11 attacks, shows the terror chief, his beard dyed black, condemning the "unjust" Iraq war and calling on Americans to "embrace Islam".

What surprised analysts was his use of the language of Left-wing protesters, which showed detailed knowledge of the economic travails of middle America.

Bin Laden referred to "the reeling of many of you under the burden of interest-related debts, insane taxes and real estate mortgage" and blamed "global warming and its woes" on "emissions of the factories the major corporations".

A former senior US intelligence official said: "It has Adam Gadahn written all over it." Mike Baker, a former CIA covert operations officer, said the tape left bin Laden with "the title of biggest gas bag in the terrorist world".

CIA officials said voice analysis of the tape proved it was definitely bin Laden.

References to the election of Nicolas Sarkozy as French president, Gordon Brown's appointment as prime minister and the anniversary of the Hiroshima bombing on August 6 led them to conclude it was filmed as recently as four weeks ago.

President Bush used the release of the tape to reinforce his view that Iraq is the central front in the war on terror.

He said: "I found it interesting that on the tape Iraq was mentioned, which is a reminder that Iraq is a part of this war against extremists.

If al-Qaeda bothers to mention Iraq, it is because they want to achieve their objectives in Iraq, which is to drive us out and to develop a safe haven."

The tape contained no direct threats, but Michael Hayden, the CIA director, gave a speech on Friday, after he was briefed on its contents, in which he said: "Al-Qaeda is focusing on targets that would produce mass casualties, dramatic destruction, and significant economic aftershocks."

American officials said the US government had obtained a copy of the video even though it had not been posted on Islamist websites - sparking speculation that US intelligence has developed an informant or cracked al-Qaeda's cyber security.

	Adam Gadahn,"Azzam The American", is the first American charged with treason since 1952

Mohamed el-Sayed, of the Ahram Centre for Political and Strategic Studies in Cairo, said bin Laden's words are proof the West cannot appease al-Qaeda by withdrawing from Iraq. "The message is much more threatening this time," he said. "It uses iconic language that suggests: 'The only way to get peace is to convert to Islam.' He's in a state of constant, unending war until he Islamises the world."

But other analysts said that the lack of specific threats is evidence that bin Laden cannot direct specific operations from his base in the tribal areas of Pakistan.

Peter Bergen, a US journalist who has interviewed bin Laden, said producing the video was a risk, as were previous audio tapes. "Every time he releases tapes he lays himself open to detection," he said.

"They are taken out by couriers from the tribal areas in Pakistan. If you can trace the train of custody of these tapes you can find bin Laden. He's keenly aware of that."