The chief prosecutor for Guantanamo's military tribunals recommended Wednesday dismissing one of eight charges against five prisoners accused over the September 11 attacks.

Brigadier General Mark Martins has asked the Pentagon official who oversees the military commissions at the US military jail to drop the conspiracy charge, while keeping intact other counts for the murders of nearly 3,000 people.

The men, whose trial is expected to get underway next year, face the death penalty.

Martins said his move was triggered by an appeals court ruling that threw out the conviction of late Al-Qaeda chief Osama bin Laden's former driver Salim Hamdan.

The US Court of Appeals in Washington said in October that a 2006 law that listed material support for terrorism as a war crime could not apply to Hamdan retroactively.

Martins indicated that there was uncertainty after that ruling about whether courts would reach a similar conclusion over allowing a stand-alone conspiracy charge for an alleged offense committed before the 2006 law.

"The withdrawal and dismissal of the conspiracy charge would remove an issue that could otherwise generate uncertainty and delay resulting from prolonged litigation in the ongoing capital prosecution of the 9/11 attacks," Martins said in a statement.

"The remaining charges are well-established violations of the law of war and among the gravest forms of crime recognized by all civilized peoples. This action helps ensure the prosecution proceeds undeterred by legal challenge."

Khaled Sheikh Mohammed, the self-proclaimed mastermind of the attacks, and his four alleged co-plotters still stand accused of seven charges that are "well-established violations of the law of war and among the gravest forms of crime recognized by all civilized peoples," Martins said.

One of the men, Mustafa al-Hawsawi of Saudi Arabia, is seeking to benefit from the court ruling that threw out Hamdan's conviction.

Australia's David Hicks, transferred back to his home country after being convicted of "material support for terrorism," is also asking that his sentence be revised after the Hamdan ruling.

If approved, the conspiracy charge could be removed as early as next preliminary hearing for the 9/11 co-plotters, to begin January 28 at Guantanamo.