NEW YORK (AFP) - The son-in-law of Osama bin Laden acted as the Al-Qaeda leader's right-hand man and appeared alongside the terror mastermind in a propaganda video just one day after the carnage of the 9/11 attacks, prosecutors said Wednesday.

Launching the most prominent 9/11-related terror trial held in New York to date, federal prosecutors said Suleiman Abu Ghaith had been one of Bin Laden's key lieutenants in the days and months after the September 11, 2001 attacks which left 3,000 people dead.

The Manhattan trial is taking just 10 blocks away from where the World Trade Center was reduced to smouldering rubble by two airliners hijacked by Al-Qaeda suicide attackers.

Abu Ghaith is on trial for conspiracy to kill Americans, conspiracy to provide support and providing material support to terrorists.

The 48-year-old from Kuwait faces life in prison if convicted and pleads not guilty to all three charges.

He is the most senior alleged Al-Qaeda member to face trial in a US federal court rather than Guantanamo Bay, which President Barack Obama has promised to close.

Wearing a dark suit, a shirt and blue silk tie, the defendant sat next to his legal team and stared at the 18-person jury as the prosecution opened their case.

He listened to proceedings through simultaneous translation into Arabic provided on an ear piece.

Abu Ghaith is not accused of planning or carrying out the 9/11 attacks, but of recruiting personnel for Al-Qaeda, or what the prosecution called its "very lifeblood".

The prosecution also claims he was complicit in the December 2001 shoe-bombing plot to bring down an airliner flying from Paris to Miami.

US prosecutor Nicholas Lewin described Abu Ghaith as a "trusted" Al-Qaeda insider who quickly met bin Laden after leaving Kuwait for Afghanistan in spring 2001.

He spent the summer of 2001 speaking to hundreds of young Al-Qaeda recruits at Afghan training camps, preparing them for war and earning his stripes.

Abu Ghaith is best known for appearing with bin Laden and the current leader of Al-Qaeda, Ayman al-Zawahiri, in an Al-Qaeda propaganda video on September 12, 2001.

Mr Lewin said he answered a personal call from bin Laden just hours after the 9/11 attacks, who wanted the "important religious scholar" and "inspirational and charismatic speaker" to recruit men globally for jihad.

"Osama bin Laden asked that man to deliver Al-Qaeda's murderous decree to the world," Mr Lewin told the court.

"What did the defendant do? He agreed." The prosecution showed the jury a blown-up screen grab of the defendant sitting next to bin Laden.

"You don't sit outside a cave on September 12, 2001 with the most wanted man on earth unless you're inside Al-Qaeda at the very, very top," added Mr Lewin. Abu Ghaith "sat at the right hand of Osama bin Laden," he added.

Married to bin Laden's daughter Fatima, US prosecutors say Abu Ghaith worked for Al-Qaeda until 2002, when he fled Afghanistan after the US invasion for Iran.

He appeared in follow-up videos in October and November 2001, an AK-47 assault rifle at his feet, threatening further attacks in a "storm of airplanes."

The trial, overseen by US District Judge Lewis Kaplan, is expected to run until the last week of March.

It is one of a series of terror cases transferred to New York as Obama has promised to close down the military prison at Guantanamo Bay.