US citizens on Sunday commemorated the 21st anniversary of the September 11 terror attacks, with President Joe Biden visiting the Pentagon and New Yorkers honoring the victims of the attacks that destroyed the Twin Towers and hit the Department of Defense.

Relatives of the victims gathered at the National September 11 Memorial in Lower Manhattan, where the names of the casualties were read about, an annual tradition carried out to commemorate the attacks.

Biden went to the Pentagon to commemorate the anniversary, as one of the planes crashed into the building that serves as the headquarters of the Department of Defense, where he addressed the families of the victims.

"Twenty-one years later, we keep alive the memory of all the precious lives stolen from us at Ground Zero, in Shanksville, Pennsylvania, and at the Pentagon," Biden said on Twitter ahead of his address at the Pentagon. 

"We will never forget," he concluded.

Twenty-one years later, we keep alive the memory of all the precious lives stolen from us at Ground Zero, in Shanksville, Pennsylvania, and at the Pentagon. To the families and loved ones who still feel the ache, Jill and I hold you close in our hearts.

We will never forget. pic.twitter.com/IZlAmyone2

— President Biden (@POTUS) September 11, 2022

Vice President Kamala Harris, Homeland Security Secretary Alejandro Mayorkas, and Mayor Eric Adams were among the dignitaries attending the ceremony held in New York.

Joe Biden's words of sympathy, however, are not enough for those affected by the attacks, as three months ago, the families of the victims called on the US President to "prioritize accountability for 9/11" in any talks he or his administration are to have with officials from Saudi Arabia or with KSA Crown Prince Mohammed bin Salman.

The open letter touched on an executive order issued by Biden to declassify a 3,000-page document related to the attack, which he said: "confirms our long-held beliefs regarding Saudi Arabia’s deep involvement in the murders of our loved ones."

The document, released on the 20th anniversary of the attacks, details multiple communications and witness testimony that prompted the FBI to suspect "Omar al-Bayoumi", allegedly a Saudi student in Los Angeles but whom the FBI suspects of being a Saudi intelligence agent. 

The families argued that the evidence uncovered in the declassified documents "underscores the importance that you do not reward the Kingdom and Crown Prince with a presidential visit that allows it to continue escaping responsibility for its role in the most horrific attack in our nation's history," ahead of Biden's visit to the country in June.

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The letter came from a group that represents some 3,000 people who had friends or family members stolen from them by the attacks that targeted the two main trade towers in the World Trade Center and the US Department of Defense, claiming the lives of 2,996 people.

Outraged by the inaction of consecutive US administrations, the families said they have watched presidents avoid the hard conversations required with Riyadh for over two decades, "and we continue to hope that you will be different."