The threat was made by Adam Gadahn, a US national who converted to Islam and became a radical supporter of Osama bin Laden, ABC said.

It said the 11-minute tape was sent to the network's office in Pakistan.

"Yesterday, London and Madrid. Tomorrow, Los Angeles and Melbourne, God willing," said the warning.

"At this time, don't count on us demonstrating restraint or compassion," the speaker added.

"We are Muslims. We love peace, but peace on our terms, peace as laid down by Islam, not the so-called peace of occupiers and dictators."

As in other recent al-Qaeda tapes, the main threats were made against the United States and Britain.

"Don't believe the lies of the liars at 1600 Pennsylvania Avenue and 10 Downing Street," the speaker said. "They have dispatched your sons and daughters to die lonely deaths in the burning deserts of Iraq and the unforgiving mountains of Afghanistan."

ABC said US intelligence believed the man who appears on the tape is Gadahn, who comes from Orange County, California. He made a similar tape last year that US intelligence said was authentic.

Los Angeles Mayor Antonio Villaraigosa and the city police department released a statement admitting that Los Angeles was a terrorist target but saying there are no known credible threats against the city.