Osama bin Laden's threats on a newly released audiotape should be taken very seriously, terrorism experts warned today.
On the tape, bin Laden warns that al Qaeda is making preparations for attacks on the United States. It appears to be the most explicit warning bin Laden has ever made of a pending attack on the United States.
"… because of God's help the mujahedin were able to penetrate all the security measures taken by the unjust coalition forces time after time," the voice on the tape says in Arabic. "The proof for that are the bombings that you saw in the capitals of the most important European countries of this hostile coalition." The tape was aired by the Arab television network al Jazeera.
"It's unlike him to say something like that," said Richard Clarke, a former White House security adviser, who is now an ABC News consultant. "It doesn't necessarily mean that he has the capability to carry it out. But it would be unusual, I think, for him to say something and not be able to back it up in some way."
The Central Intelligence Agency confirmed the tape contained the voice of bin Laden, although his voice sounded weak and less robust than in his last audiotape, which surfaced in late December 2004. Previous such tapes have proved to be authentic.
The tape's release came after a U.S. airstrike in Pakistan that targeted bin Laden's deputy, Ayman al-Zawahri. Four leading al Qaeda figures, including possibly Zawahri's son-in-law, were killed. There was no mention of the attack on the segments that were broadcast on al Jazeera.
It was the first purported tape from bin Laden in more than a year -- the longest period without a message since the Sept. 11, 2001, suicide hijackings in the United States.
Al-Jazeera said the tape was recorded in the Islamic month that corresponds to December.
The male voice on the tape goes on to say: "There is no way to end the war in Iraq and Afghanistan. Our situation is very good; yours is very bad."
The speaker then suggests a truce is possible.
"We have no objection to a long-term truce with you based on fair conditions that we would fulfill," the voice on the tape said. "We are a nation prohibited by God from deceit and lying. During this truce, the two sides will enjoy security and stability, and so we can build Iraq and Afghanistan, which were destroyed by the war."
White House spokesman Scott McClellan said during a press conference today that talk of a truce was a sign of weakness.
"We do not negotiate with terrorists," he said. "We put them out of business."
Fawaz Gerges, a professor of Middle Eastern Studies at Sarah Lawrence College and an ABC News consultant, said the tape would inspire bin Laden's followers, however.
"The rank and file of al Qaeda -- the supporters, the hardcore -- will be delighted, inspired because there has been a great deal of speculation," said Gerges. "People were concerned about the fate of Osama bin Laden. So what the tape does is provide inspiration."
There are currently no plans to raise the terror threat level.
ABC News' Brian Ross contributed to this report.