Technical analysis of an audio tape aired earlier this week on the al-Jazeera satellite network shows "almost certainly" it is of al-Qaeda leader Osama bin Laden, US intelligence has concluded.

The technical analysis tells us it is almost certainly bin Laden US intelligence official

Unnamed officials told the US media analysis of the tape by the intelligence experts has now been completed, confirming earlier conclusions about the authenticity of the recording.

The 16-minute message was broadcast on al-Jazeera on Tuesday, in which a man's voice, alleged to be bin Laden's, is heard calling for suicide attacks against the US and resistance to any attack on Iraq.

It was aired on the same day that the head of the CIA, George Tenet, warned of an increased risk of al-Qaeda attacks in the US and on the Arabian peninsula.

The Bush administration has already said the tape was almost certainly genuine, adding that it heralded a "burgeoning alliance of terror".

'Sophisticated means'

The message was contained in a poor quality audio recording, but a US official told Reuters news agency it was of better quality than a previous tape released last November.

We stress the importance of martyrdom attacks against the enemy Voice identified as Osama Bin Laden

Click here for excerpts for Bin Laden message

"The technical analysis tells us it is almost certainly bin Laden," the official said.

Another US official said "fairly sophisticated" means were used to compare the audio with past samples known to be of bin Laden's voice.

'Specific threats'

The tape was aired as Mr Tenet and FBI Director Robert Mueller said US intelligence had pointed to possible terror in a matter of days.

They said such attacks could possibly involve using chemical or nuclear weapons.

"The intelligence is not idle chatter on the part of terrorists and their associates," Mr Tenet said.

"It is the most specific we have seen, and it is consistent with both our knowledge of al-Qaeda's doctrine and our knowledge of plots this network - and particularly its senior leadership - has been working on for years."