Osama bin Laden's son-in-law has pleaded not guilty to plotting against Americans in his role as al Qaeda's leading spokesman as a landmark case trying a terror suspect on US soil moves forward.

Sulaiman Abu Ghaith entered the plea to one count of conspiracy to kill Americans after being captured in Jordan in the past week.

The case marks a legal victory for the Obama administration, which has long sought to charge senior al Qaeda suspects in US federal courts instead of holding them at the military detention centre at Guantanamo Bay, Cuba.

Charging foreign terror suspects in federal courts was a top pledge by President Barack Obama shortly after he took office in 2009 – aimed, in part, to close Guantanamo Bay.

Attorney General Eric Holder had announced the capture of Abu Ghaith, saying "no amount of distance or time will weaken our resolve to bring America's enemies to justice".

The Justice Department said former mosque preacher Abu Ghaith was the spokesman for al Qaeda, working alongside bin Laden and current leader Ayman al Zawahiri, since at least May 2001.

The day after the September 11 attacks, prosecutors say he appeared with bin Laden and al Zawahiri and called on the nation of Islam to battle against Jews, Christians and Americans.

Abu Ghaith nodded yes when asked, through an interpreter, if he understood his rights.

He shook his head when asked whether he had money to hire a lawyer.

Bail was not requested and none was set. The judge said he would set a trial date for April 8. Prosecutors said a trial would last about three weeks.