<br/>The Al-Qaeda Chief Osama bin Laden has threatened to execute any Americans taken prisoner by it, if accused 9/11 mastermind Khalid Sheikh Mohammed is executed. Bin Laden, in a new audio message, said that the day the US takes the decision to execute Sheikh Mohammed and his conspirators; al-Qaeda will also take the decision that any of American falling into its hands will be executed.<br/> Sheikh Mohammed is accused of masterminding the Sept. 11, 2001 attacks on New York and Washington that took nearly 3,000 lives. The alleged architect of terror was captured in Pakistan in 2003.