Bin Laden: We Will Execute Americans If You Harm KSM U.S. official calls Osama's threat the 'height of absurdity.'

March 25, 2010  -- In an audiotape released Thursday, Osama bin Laden threatened to kill any captured Americans if the U.S. government executes accused 9/11 mastermind Khalid Sheikh Muhammad.

U.S. officials are trying to authenticate the message, but believe it is in fact bin laden's message.

A U.S. counterterrorism official quickly responded to bin Laden's message, telling ABC News, "It's the height of absurdity for anyone associated with al-Qaeda to even suggest that -- now, at long last -- they're going to start treating captives badly. They may have forgotten Danny Pearl and all the others they've slaughtered, but we haven't."

"If this is Bin Laden and he wants to weigh in on legal proceedings involving 9/11 conspirators, I challenge him to show up in court to make his case," the official added. "Frankly, that's about all the comment this deserves."

The message first aired on Al-Jazeera television. In the message, bin Laden said al Qaeda would take revenge against Americans if Muhammad, who has taken credit for planning the 9/11 attacks, or any other al Qaeda operatives in U.S. custody were to be executed.

U.S. military officials believe an American soldier captured in Afghanistan in 2009, Pfc. Bowe Bergdahl is currently being held by an al Qaeda-affiliated insurgent group in Pakistan's tribal areas.

Muhammad and four other senior al-Qaeda members are expected to be prosecuted for their roles in the 9/11 attacks after being held for years at Guantanamo. This is the first bin Laden message since late January, when he addressed the Palestinian struggle against Israel.

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