However, the Saudi government has long denied any involvement. The Saudi embassy in Washington on Wednesday said it supported a complete declassification of all records “as a way to eliminate baseless allegations against the kingdom once and for all.” The embassy said any allegations made by Saudi Arabia were “clearly false.”

Biden last week ordered the Justice Department and other agencies to review the declassification of investigative documents and release what they can within the next six months.

The 16-page release was released Saturday night, just hours after Biden attended the September 11 commemorations in New York, Pennsylvania and Northern Virginia. Relatives of the victims – who are demanding billions of dollars from Saudi Arabia – had previously objected to Biden’s presence at official ceremonies as long as the documents were classified.

The heavily redacted FBI record describes an interview in 2015 with a man applying for US citizenship and years of repeated contacts with Saudi nationals whom investigators said were linked to several hijackers and who may have rovided “critical logistical support”.

The entire document keeps the identity of the man unknown, but describes him as working at the Saudi consulate in Los Angeles. According to the document, his contacts included a Saudi citizen named Omar al-Bayoumi. Al-Bayoumi, who had ties to the Saudi government, helped two hijackers find and lease an apartment in San Diego shortly after arriving in Southern California.

Al-Bayoumi called his restaurant meeting with hijackers Nawaf al-Hazmi and Khalid al-Mihadhr in February 2000 a “face-off”, and the FBI made several attempts during his interview to determine if the feature was correct. 

The document states that “Bayoumi’s participation and assistance to Mahdi includes translation, travel, housing and financial assistance.” The document cites Fahd al-Thomiri, then a credible diplomat at the Saudi consulate in Los Angeles, who, according to investigators, led a hardline faction in his mosque.

Relatives of the victims described the release of the document as an important step in trying to link the attacks to Saudi Arabia.

Brett Eagleson, whose father, Bruce, was killed in the World Trade Center attack, said the release of FBI material “accelerates the pursuit of truth and justice.”

The United States has previously investigated links between some Saudi diplomats and other Saudi government officials who knew the hijackers when they arrived in the United States. But the FBI’s 9/11 Commission’s report found “no evidence that the Saudi government, as an organization or as a senior Saudi official, individually financed the attacks”.

However, the commission noted the “possibility” of Saudi-run charities. The new documents are being released at a politically critical time for the United States and Saudi Arabia, two countries that have forged a strategic – if difficult, alliance, especially on counterterrorism issues.