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The tape, released on Friday, ends with bin Laden telling US citizens that they should "embrace Islam" if they want the war in Iraq to end.
According to a transcript released by a US-based website which monitors radical websites, bin Laden suggests that there are two ways the Iraq war could be ended.
|Extracts from bin Laden's video address|
"The first is from our side, and it is to continue to escalate the killing and fighting against you," he said.
The second is for the US to abandon its democratic system of government.
He said that US Democrats had failed to stop the Iraq war because of the power of US corporations.
"The mistakes of Brezhnev are being repeated by Bush," Bin Laden said on the tape, in a reference to the Soviet invasion of Afghanistan which began in 1979.
He said the war in Iraq was continuing for "the same reasons which led to the failure of former president [John F] Kennedy to stop the Vietnam war - those with real power and influence are those with the most capital".
Commenting on the video from Sydney, Australia, where he is attending the Apec forum summit, Bush said the tape was "a reminder about the dangerous world in which we live, and it is a reminder that we must pull together to protect our people against these extremists who murder the innocent in order to achieve their political objective.
"If al-Qaeda bothers to mention Iraq, it's because they want to achieve their objectives in Iraq, which is to drive attacks and develop a safe haven."
"Osama has never been a threat to anyone's security, just for those who are aggressors"
Euhunza, Karachi, Pakistan
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The tape was released in advance of a testimony on Monday by General David Petraeus, the senior US commander in Iraq, and Ryan Crocker, the US ambassador to Iraq, on the status of the so-called surge of US troops in Iraq.
In the video, bin Laden is shown with his beard much shorter and darker than in his last appearance, when it was streaked with grey.
A banner on the screen reads in English: "A message from Sheikh Osama bin Laden to the American people."
Authenticity A US intelligence official told AFP news agency that the tape was probably produced as recently as early August because of a reference to the 62nd anniversary of the bombing of Hiroshima on August 6.
"I think people are pretty confident it is his voice," the intelligence official said on condition of anonymity said.
References in the video to Nicolas Sarkozy, the French president, and Gordon Brown, the British prime minister, are also believed to suggest that the video is only a few weeks old.
Adel Darwish, political editor of Middle East magazine, told Al Jazeera that he had "doubts" about the authenticity of the tape.
"Any kid these days with an electronic kit can alter images and edit the way that he or she likes," he said on Friday.
"There is no close-up of bin Laden, the beard is thick and black and then there are large segments where the image is a still."
Marwan Bishara, Al Jazeera's senior political analyst, said bin Laden had released the video to tell the Americans that he was still alive and still leading.
"[The tape] underlines the strength of words in this new asymmetrical warfare in the 21st century between the US and al-Qaeda," he said.
Bin Laden was last seen in a video statement shortly before the US presidential election in 2004.
Since then, he has issued a number of audio messages, the last in July 2006 when he vowed al-Qaeda would fight the US across the world.