Biden orders release of secret 9/11 documents

US President Joe Biden on Friday ordered declassification over the next six months of still secret documents from the government investigation into the 9/11 terrorist attacks.

Biden is responding to pressure from families of some of the approximately 3,000 people killed by Al-Qaeda on September 11, 2001.

They have long argued that the classified documents might contain evidence that the government of Saudi Arabia, a close US ally, had links to the hijackers who flew into the World Trade Center and Pentagon.

"Today, I signed an executive order directing the Department of Justice and other relevant agencies to oversee a declassification review of documents related to the Federal Bureau of Investigation's September 11th investigations," Biden said in a statement.

Declassification must take place "over the next six months."

"We must never forget the enduring pain of the families and loved ones of the 2,977 innocent people who were killed during the worst terrorist attack on America in our history," Biden said.

The move comes ahead of the 20th anniversary of the attack, which spurred then-president George W Bush soon after to order the invasion of Afghanistan, where the Taliban sheltered al-Qaeda's leadership.

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.

Some of the investigation may still be deemed too sensitive to release.