Al Qaeda leader Osama Bin Laden’s spokesman and son-in-law has pleaded not guilty to plotting to kill Americans in a federal court in New York.

Sulaiman Abu Ghaith appeared in a dark blue prison smock and handcuffs. He is thought to have been captured in Jordan by US agents.

Ghaith will be the closest of bin Laden’s confidantes to face trial in a US federal court.

His capture is a major coup for the US. He was never an operational commander but an ideologue and preacher whose fiery online sermons inspired others to attempt attacks, say US officials.

Prosecutors say Ghaith was the spokesman for bin Laden. The day after the 9/11 attacks, prosecutors say, he called on the “nation of Islam” to battle against Jews, Christians and Americans, warning them “a great army is gathering against you”.

He was one of the founding inner circle of al Qaeda – a position he strengthened by marrying one of bin Laden’s daughters. He could yield valuable information under interrogation about the network.

Ghaith’s case is a victory for the Obama administration, which has long sought to charge and try al Qaeda figures in US federal courts instead of the military tribunals at Guantanamo Bay, Cuba.

President Obama promised to close down the Guantanamo detention centre, but failed to do so in the face of fierce opposition by Republicans.

Khalid Sheikh Mohammed, the alleged mastermind of the 9/11 attacks, is on trial there with four alleged accomplices after the failure to bring them to trial in mainland America.

Ghaith appeared in court a few blocks from Ground Zero, where the twin World Trade Centre towers stood until the 9/11 attacks.

So far his appearance has not aroused any significant protest from New York residents, although some Republicans in Congress have called for him to be tried at Guantanamo.

Ghaith’s activities over the last decade is the subject of debate. He is believed to have lived in Iran for much of that time.

Iranian sources have said he was held in jail there for years. But US media reports claim he was free to operate an al Qaeda cell funnelling money and weapons over the border and into Afghanistan.

He was reportedly arrested first in Turkey where authorities reportedly claimed there was insufficient evidence to extradite him to the US.

He is thought to have been captured by US agents in Jordan while en route to Kuwait after being deported from Turkey.

Bail was not requested during Friday’s proceeding and none was set. The judge scheduled an April 8 trial date, which prosecutors expect to last about three weeks.