A new tape said to have been made by Osama Bin Laden is probably genuine, CIA experts have reportedly concluded.
The recording, broadcast by an Arabic TV channel on Saturday, contains a call for Islamic "holy war" and a threat of new suicide attacks on America.
"We assess the voice was likely that of Osama Bin Laden," a CIA source told reporters on condition of anonymity.
The al-Qaeda leader has long been thought either dead or in hiding since he lost his power base in Afghanistan.
No video tapes of him speaking have been produced since the US-led war in Afghanistan sparked by the 11 September 2001 attacks on America - which Bin Laden allegedly masterminded.
Analysts from the US Central Intelligence agency who studied the new tape, aired by al-Jazeera satellite TV, said it appeared to have been made in the past six months because of references to recent events in the Middle East.
The new message calls on Muslims around the world to wage a jihad, or holy war, on America and its allies for invading Iraq.
It also pledged "martyrdom operations inside and outside the United States" - the term commonly used for suicide attacks - and named as targets both America and its allies Britain, Spain, Australia, Poland, Japan and Italy, as well as a number of Gulf states.
Speaking before the new tape was verified, US President George W Bush described it as proof "the war on terror goes on, that there's still a danger to free nations".