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Barack Obama suggested last night that removing Osama bin Laden from the battlefield was no longer essential and that America's security goals could be achieved merely by keeping al-Qaeda "on the run".

"My preference obviously would be to capture or kill him," he said. "But if we have so tightened the noose that he's in a cave somewhere and can't even communicate with his operatives then we will meet our goal of protecting America."

His comments, in a CBS interview, represent a significant watering down of the "dead or alive" policy pursued by President Bush since the terror attacks of September 11, 2001. They also appear to contradict Mr Obama's own statements made in the election campaign.

As recently as October 7, in a presidential debate, Mr Obama said: "We will kill bin Laden. We will crush al-Qaeda. That has to be our biggest national security priority."

Yesterday, the President-elect adopted far less aggressive language, saying his "No 1 priority" was to protect America from further attack.

"I think that we have to so weaken [bin Laden's] infrastructure that, whether he is technically alive or not, he is so pinned down that he cannot function," he said. "And I'm confident that we can keep them on the run and ensure that they cannot train terrorists to attack our homeland."

A new audio tape thought to be from bin Laden was broadcast yesterday, taunting President Bush for leaving his successor "with a heavy inheritance" that would force Mr Obama to choose between military defeat or drowning in economic crisis.

Asked about the tape, Mr Obama confirmed that the focus of his national security priority would be Afghanistan and the border region with Pakistan, saying: "We took our eye off the ball when we invaded Iraq."

He added: "We have to put as much pressure on them as possible. I've already spoken to my National Security team about how we're going to do that."

The White House has dismissed the latest propaganda shot from al-Qaeda, saying that it reflected bin Laden's "isolation" and desperation to remain relevant at a time when his ideology and mission were being challenged.

The tape, entitled "a call for jihad to stop the aggression on Gaza," was played over a still picture of bin Laden and the Al-Aqsa Mosque in Jerusalem's Old City, one of Islam's holiest sites.

Pointing to wars in Afghanistan and Iraq since the September 11, 2001, attacks, bin Laden said that al-Qaeda was prepared to fight "for seven more years, and seven more after that, then seven more...we are on the way to opening new fronts".

He urged Muslims to "join hands with the Mujahidin to continue the jihad against the enemy, to continue bleeding them", adding: "The question is, can America continue the war against us for several more decades? The reports and signs show us otherwise."

Joe Biden, the Vice President-elect, briefed Mr Obama yesterday after spending this week on a Senate fact-finding mission to Iraq and Afghanistan.

He said: "Things are going to get tougher in Afghanistan before they get better. There needs to be more resources to attend to in the situation of Afghanistan."

Dick Cheney, the Vice-President, has recently stated he still hopes to capture or kill bin Laden before leaving office. "We've got a few days left yet," he said on Friday.

Last night, however, in another round of interviews, Mr Cheney cited the containment of the terror network as an important achievement of the past seven years.

"Osama bin Laden is — wherever he is — he's in a deep hole. He does not have much impact on the organisation as best we can tell. The important thing was to go after the organisation, after al Qaeda," he said.

"Even if you got Osama bin Laden tomorrow, you'd still have a problem in terms of whatever residue of al-Qaeda is out there.

"The situation now obviously is that we've got to continue to be engaged in Afghanistan. It's one of the most difficult places to work in because of the territory, the geography, the terrain, but also because it's one of the poorest countries in the world."

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