Nearly 3,000 people died in the attacks, when al Qaeda hijackers flew planes into the New York's World Trade Center towers and into the Pentagon in Arlington, Virginia, while a fourth plane crashed in Pennsylvania.

Passengers on United Airlines Flight 93 overcame the hijackers and the plane crashed in a field, preventing another target from being hit.

Biden also met with members of the Association of Flight Attendants-CWA at the memorial, hugging some of them.