President-elect Barack Obama said Wednesday that Al-Qaeda and Osama bin Laden remain the "number one threat" to US security, after the elusive militant leader warned of new fronts in his war on the West.

In his first audio commentary in eight months, bin Laden called on all Muslims to take revenge against Israel for its deadly offensive in Gaza, charging the onslaught had been timed to take advantage of the dying days of George W. Bush''s presidency.

"Bin Laden and Al-Qaeda are our number one threat when it comes to American security," Obama told reporters after the emergence of the 22-minute audio recording entitled "A Call for Jihad to Stop Aggression Against Gaza."

"We''re going to do everything in our power to make sure that they cannot create safe havens that can attack Americans. That''s the bottom line," added Obama.

The US-based Site Intelligence Group said it believed the recording, in which bin Laden crows at the legacy that Bush is leaving Obama, was authentic.

The White House declined to immediately authenticate the statement as being from the man who carries a 25-million-dollar bounty on his head.

But spokesman Gordon Johndroe said: "It appears this tape demonstrates his isolation and continued attempts to remain relevant at a time when Al-Qaeda''s ideology, mission, and agenda are being questioned and challenged throughout the world."