SAUDI Arabian diplomat Mussaed Ahmed al-Jarrah has “mistakenly” been named by the FBI as one of those suspected of aiding two of the al-Qaida hijackers responsible for the September 11 terror attacks in New York.

FBI counterterrorism unit assistant director Jill Sanborn made the declaration in response to a long-running lawsuit by relatives of those who died in the 2001 attack on the World Trade Centre.

They insist that the Saudi government was involved in the attacks, which killed nearly 3,000 people after two airliners were hijacked and deliberately crashed into the Twin Towers nearly 19 years ago.

A third jet hit the Pentagon in Washington DC, while passengers on a fourth flight fought to wrest back control from terrorists before the plane came down in a Pennsylvania field, killing all on board.

Mr Jarrah was a Saudi Foreign Ministry official and was based at the Gulf kingdom’s embassy in Washington between 1999 and 2000.

According to the report, he was responsible for overseeing employees of the Ministry of Islamic Affairs working at mosques and Islamic centres in the US.

The FBI believes that Mr Jarrah instructed two people, named as cleric Fahad al-Thumairy and suspected Saudi agent Omar al-Bayoumi, to help settle two of the hijackers in the US in January 2000.

But the declaration was removed from the public file on Monday at the request of Justice Ministry officials. The report now states that the document was “incorrectly filed in this case.”

Spokesman for the families Brett Eagleson said: “This shows there is a complete government cover-up of the Saudi involvement. This is a giant screw-up.”

Yahoo News investigative journalist Michael Isikoff, who broke the story, said that he knew as soon as he saw the document that there had been a blunder.

"When I noticed that the declaration included this information, I contacted the FBI for comment, because I knew that the Justice Department and the Trump administration had been going to extraordinary lengths to keep all of this under wraps," he said.

"In fact, both Attorney General William Barr and the acting Director of National Intelligence Richard Grennell had filed motions with the court saying that any information relating to the Saudi embassy official and all internal FBI documents about this matter were so sensitive, they were state secrets. That means, if revealed, they could cause damage to the national security.”

Riyadh has long enjoyed immunity from prosecution for the September 11 attacks. But in 2017, Congress overturned former president Barack Obama’s veto, opening the way for lawsuits under the Justice Against Sponsors of Terrorism Act.

Saudi Arabia is currently being sued for billions of dollars by the families of roughly 2,500 of those killed and more than 20,000 people who suffered injuries, along with businesses and various insurers.