Al-Qaida leader Osama bin Laden threatened in a new audio recording released Thursday to kill any captured Americans if the U.S. executes the self-professed mastermind of the Sept.11 attacks or any other al-Qaida suspects.

The U.S. is still considering whether to put Khalid Sheik Mohammed and four of his fellow plotters on military tribunal for their role in the Sept. 11 attacks. The Obama administration is also looking into recommendations for civilian trials, and is expected to announce a decision soon.

In a brief 74-second audio tape aired on Al-Jazeera television, bin Laden said if the U.S. decides to execute any al-Qaida suspects in its custody — and explicitly mentioned Mohammed — his terror network would kill American captives.

The terror leader said such a decision "would mean the U.S. has issued a death sentence against whoever of you becomes a prisoner in our hands."

It was not immediately clear whether al-Qaida is currently has any US captives, but the Haqqani group — the Pakistan-based Taliban faction closest to al-Qaida — is holding an American soldier it captured in eastern Afghanistan in June 2009. It released a video of him in December.

Bin Laden said U.S. President Barack Obama is following in the footsteps of his predecessor George W. Bush by escalating the war in Afghanistan, being "unjust" to al-Qaida prisoners and supporting Israel in its occupation of Palestinian land.

In a veiled threat, bin Laden said Americans had previously thought their homeland was beyond the reach of his group until the 9/11 attack.

Mohammed, who was captured in Pakistan in 2003, is the most senior al-Qaida operative in U.S. custody, and is currently in detention at the U.S. naval base at Guantanamo Bay, Cuba. In 2008, the U.S. charged him with murder and war crimes in connection with the Sept. 11 attacks. Pentagon officials have said they'll seek the death penalty.