CIA analysis suggests a new audiotape purportedly recorded by al-Qaeda leader Osama Bin Laden is genuine.
Arabic television has aired several 'Bin Laden' tapes
A CIA source told the BBC the finding was based on technical analysis of the tape, which was broadcast on Sunday.
If authentic, it would be the first time Bin Laden has been heard from since a previous tape attributed to him was broadcast last October.
Correspondents say it shows the world's most wanted man seems to still be able to get his message out to the world.
The conclusion of the CIA was backed by the US Director of Homeland Security, Tom Ridge.
"Preliminary assessments says this is the voice of Osama Bin Laden," Mr Ridge told US television network CBS.
UK Foreign Secretary Jack Straw also said the tape - broadcast by Arabic satellite channel al-Jazeera - is probably genuine.
"I've had no confirmation, but let's for the purpose of this interview assume that it was him," Mr Straw told the BBC.
"So far as we know, Osama Bin Laden is still alive."
The 14-minute recording is the first supposed Bin Laden tape to be aired by al-Jazeera since 18 October, 2003.
In the latest recording, the speaker obliquely refers to an unofficial peace plan for the Middle East launched in Geneva early in December, and the capture of Saddam Hussein on 13 December.
A voice purported to belong to Bin Laden has made more general references to events in previous tapes, such as US forces fighting insurgents in Iraq, in the October broadcast.
In a tape aired in September, the speaker praised the hijackers who carried out the attacks on the United States two years earlier.
The BBC's security correspondent, Frank Gardner, says Bin Laden appears to be continuing to get his message out to the world by having tapes smuggled out of his hideaway by hand.
He says they can also be broadcast untraced to millions of listeners over the internet.
The voice on the tape urges Muslims to fight "occupiers" and condemns Arab states which backed the US invasion of Iraq.
"There can be no dialogue with occupiers except through arms. This is what we need today and what we should seek...
"The occupation of Iraq is the beginning of the full occupation of the other Gulf states... because of the presence of the biggest deposits of oil," the speaker says.
He berates Gulf leaders who "succumbed to US pressure and opened their air, land, and sea bases to contribute toward the US campaign, despite the immense repercussions of this move".
Referring to the arrest of Saddam Hussein, the voice on the tape says Arab rulers now fear that dictatorial regimes can be overthrown "by armed force from abroad, especially after they have seen the arrest of their former comrade" .