US intelligence officials say the voice on an audio recording broadcast on Arabic television last week is almost certainly that of Osama Bin Laden.

White House spokesman Scott McClellan said experts who have analysed the recording believe it is authentic and was made in the past few weeks.

Our intelligence experts do believe that the tape is genuine

Scott McClellan, White House spokesman

The speaker on the recording praised recent terror attacks against Western targets and made threats against countries which supported the United States.

It is the clearest indication for nearly a year that Osama Bin Laden is alive.

The al-Qaeda leader's fate has been the centre of intense speculation since he was last heard of with some certainty in December 2001.

Clues sought

The tape, which was broadcast by the Qatar-based al-Jazeera satellite channel on 12 November, has been analysed by the CIA and the National Security Agency, which listens to communications around the world.

Bin Laden was last reported alive in Tora Bora

"Our intelligence experts do believe that the tape is genuine," said Mr McClellan.

"It cannot be stated with 100% certainty. It is clear that the tape was made in the last several weeks," he said.

An intelligence official told Reuters news agency that experts would continue to examine the tape "and the circumstances surrounding it" to try to glean additional clues as to Bin Laden's whereabouts.

Al-Jazeera television did not say how it obtained the tape, which was apparently recorded over a telephone line.

Attacks praised

The voice on the tape praised anti-Western attacks as recent as last month, including the Bali bombing; the killing of a US marine in Kuwait; the bombing of a French oil tanker off the coast of Yemen; and the siege of a Moscow theatre by Chechen rebels.

You will be killed just as you kill

Voice on tape

It spoke of "the raids on New York and Washington" - an apparent reference to the 11 September attacks, widely blamed on Bin Laden and al-Qaeda.

The speaker warned that America's allies - specifically Britain, France, Italy, Canada, Germany and Australia - would also be targeted if they continued to support Washington.

"You will be killed just as you kill," he said.

Chilling reminder

The audio tape has heightened concern that al-Qaeda might be planning more large scale attacks.

Mr McClellan said the tape's existence was a "reminder that we are at war with terrorism".

Bin Laden was last reported alive in mid-December 2001, when US intelligence detected his voice in radio messages from Afghanistan's Tora Bora cave complex.

US officials believe that if he is alive, the al-Qaeda chief is probably in hiding along the Afghanistan-Pakistan border.

The US has offered a $25m reward for information leading to Bin Laden's whereabouts.