New York, Aug. 29 -- A US military judge has ruled that confessions made by alleged September 11 mastermind Khalid Sheikh Mohammed to FBI agents in 2007 are inadmissible at trial, finding that the statements were not made voluntarily, according to media reports.

The ruling is a setback for the US government's long-running effort to prosecute Mohammed, also known as KSM, who is accused of helping organise and direct the plot to hijack four commercial aircraft and crash them into the World Trade Centre and the Pentagon. Nearly 3,000 people were killed in the September 11, 2001 attacks.

Military judge Lt Col Michael Schrama ruled that statements Mohammed made during four days of questioning at Guantanamo Bay in January 2007 could not be used...