The order is a significant moment in a years-long tussle between the government and the families over what classified information about the run-up to the attacks could be made public.
US President Joe Biden has ordered reviews of the potential declassification of documents from the FBI's investigation into the September 11, 2001, attacks on the United States.
"When I ran for president, I made a commitment to ensuring transparency regarding the declassification of documents on the September 11, 2001 terrorist attacks on America," Biden said in a statement on Friday. "As we approach the 20th anniversary of that tragic day, I am honoring that commitment."
Biden said his order directed the Department of Justice and other agencies to "oversee a declassification review of documents" related to the FBI probe. The order requires Attorney General Merrick Garland to make the declassified documents public over the next six months, he said.
Victims families seek information amid lawsuit against Saudi Arabia
Family members of victims of the September 11 attacks asked a US government watchdog on Thursday to investigate their suspicions that the FBI lied about or destroyed evidence linking Saudi Arabia to the hijackers.
The request in a letter to Department of Justice Inspector General Michael Horowitz said "circumstances make it likely that one or more FBI officials committed willful misconduct with intent to destroy or secrete evidence to avoid its disclosure."
The push for more information is being driven by victims' families suing Saudi Arabia for alleged complicity in the horrific attack. The families have long expressed frustration at the number of documents that remain off limits.
The lawsuit took a major step forward this year with the questioning under oath of former Saudi officials, and family members have long regarded the disclosure of declassified documents as an important step in making their case.
Fifteen of the hijackers were Saudi, as was Osama bin Laden, whose Al Qaeda network was behind the attacks.
READ MORE: Al Qaeda: Ten years after Osama bin Laden
Particular scrutiny has centered on the support offered to the first two hijackers to arrive in the US, Nawaf al Hazmi and Khalid al Mihdhar, including from a Saudi national with ties to the Saudi government who helped the men find and lease an apartment in San Diego and who had earlier attracted FBI scrutiny.
The official 9/11 Commission, which was set up by Congress, said there was "no evidence that the Saudi government as an institution or senior Saudi officials individually funded" Al Qaeda.
That phrasing has been interpreted by some as suggesting that unofficial or lower ranking Saudi figures might have played a role.
The Saudi government has denied any connection to the attacks.