PRESIDENT Joe Biden has been told by families of the victims of the 9/11 terrorist attacks in 2001 to stay away from next month’s 20th anniversary commemorations as the US government continues to withhold documents about the atrocity.

Nearly 3000 people died on September 11, 2001, in the worst terrorist outrage on American soil.

Al-Qaeda suicide pilots crashed four passenger jets into the two towers of New York’s World Trade Centre, the Pentagon at Washington and a Pennsylvania field.

In a letter released yesterday, some 1700 signatories – including survivors and first responders – expressed the anguish of the victims who have not been able to get the documents which they claim show the involvement of Saudi Arabia in the attack.

They are angered that Biden has not fulfilled his commitment to more transparency. Like the previous three presidents, his administration has cited national security reasons for keeping the files secret.

“Twenty years later, there is simply no reason – unmerited claims of ‘national security’ or otherwise – to keep this information secret,” the letter stated.

“But if President Biden reneges on his commitment and sides with the Saudi government, we would be compelled to publicly stand in objection to any participation by his administration in any memorial ceremony of 9/11.”

In an earlier statement the group said: “We cannot in good faith, and with veneration to those lost, sick, and injured, welcome the president to our hallowed grounds until he fulfils his commitment.

“Since the conclusion of the 9/11 Commission in 2004 much investigative evidence has been uncovered implicating Saudi government officials in supporting the attacks.

“Through multiple administrations, the Department of Justice and the FBI have actively sought to keep this information secret and prevent the American people from learning the full truth about the 9/11 attacks.”

In total 15 of the 19 hijackers were from Saudi Arabia. The US government commission found no evidence that Saudi Arabia directly funded Al-Qaeda.

Khalid Sheikh Mohammed, the American-educated Pakistan-born Islamist, is accused of being the mastermind behind 9/11. He has been held in Guantanamo Bay since 2003 and is awaiting trial later this year.

Al-Qaeda’s leader at the time of the 9/11 bombings was Osama bin Laden, son of a wealthy Saudi Arabian father. He was hunted for many years before being killed in a raid in Pakistan by US Special Forces in 2011.

It is known that there was a comprehensive FBI investigation into the attacks that examined alleged Saudi links and was completed in 2016. It is the documents linked to that investigation which the group wants to see, not least because many of them have raised federal lawsuits seeking reparation from Saudi Arabia.

The Saudi government has always denied any involvement with Al-Qaeda but there is strong evidence that the terrorists were funded by Saudi nationals.

Brett Eagleson, who was a teenager when his father was killed during the attacks, told NBC he is certain the classified documents would reveal the involvement of senior officials in the Saudi government.