In a setback for President Barack Obama, Democrats, still controlling the House, have approved legislation to prevent Khalid Sheikh Mohammed and other detainees at the military prison at Guantanamo Bay from being transferred to the US for trials in criminal courts.
The Guantanamo ban was included in a huge catchall spending bill that passed the House Wednesday by a 212-206 vote. The Senate has yet to act on the legislation, which would further imperil Obama's effort to close the detention centre for terrorist suspects.
The move comes after the first Guantanamo detainee to face a civilian trial, Ahmed Ghailani, was found guilty last month of just one of the hundreds of charges brought against him in connection to the 1998 attacks on two US embassies.
Although Ghailani faces up to life in prison, Republican lawmakers pointed to the case as a reason to support military trials for the Guantanamo detainees.
Wednesday's vote would block alleged 11 September 2001 mastermind Khalid Sheikh Mohammed from a civilian trial.
Critics of the administration's approach also argue that civilian courts are more likely than military courts to hand down acquittals because of more lenient rules of evidence and rights afforded to suspects.
The legislation goes beyond current law, which allows detainees to be transferred to the United States for trial but not to be released.
The provision is opposed by the Obama administration, which made some gains with the underlying budget bill which designated a sum of money for the implementation of a recent nuclear weapons treaty with Russia and a signature education initiative.
When Obama took office almost two years ago, he pledged to close the prison by early 2010. The promise soon unravelled amid resistance from Democrats and a politically charged opposition from Republicans.
The transfer ban would apply until 30 September -- the end of the fiscal year.