The White House says a new video by Osama bin Laden shows the Al-Qaeda mastermind as an "impotent" figurehead who poses little threat to the US.
Frances Townsend, President George W Bush's homeland security advisor, said the US intelligence community "believes it is bin Laden" following analysis of the tape, which surfaced Friday.
"The indications from the contents of the tape are that it was made recently. Certainly in the last several months," she said on Fox News.
"There's nothing overtly obvious in the tape that would suggest that this is a trigger for an attack," Mr Townsend added.
"This is about the best he can do. This is a man on the run from a cave who is virtually impotent other than these tapes.
"We know Al-Qaeda is still determined to attack. We take it seriously, but this tape appears to be nothing more than threats. It's propaganda on their part."
But Democrats highlighted the tape as proof for their contention that Iraq has been a dangerous distraction from the "war on terror."
"This is an insult to everybody in the world that this man is still sending his tapes," Senator John Kerry, Bush's opponent in the 2004 election, said on ABC television.
"And it is the real failure because Iraq had nothing to do with Osama bin Laden in the beginning," he said.
In the tape, the Al-Qaeda leader marks six years since the 2001 terrorist strikes on the World Trade Center and the Pentagon with a call for an escalation of the insurgency in Iraq.
Bin Laden says there are two ways to end the Iraq war. "The first is from our side, and it is to continue to escalate the killing and fighting against you," he says.
The second is to do away with the US democratic system of government, which he says merely serves the interests of major corporations.
Bin Laden also invites Americans to embrace Islam.
The tape surfaced before a week of drama in Washington as General David Petraeus and Baghdad ambassador Ryan Crocker, the top two Americans in Iraq, prepare to testify in Congress today and tomorrow.
Mr Bush said Saturday that the new video showed how dangerous the world remains and how the United States must show resolve in Iraq.
It was bin Laden's first such appearance since October 2004, when he threatened new attacks against the United.
"Capturing and killing bin Laden is the number one priority, but it's not our only priority. We also have to be mindful of current ongoing threats against this country," Ms Townsend told CNN.