Queen Elizabeth said earlier on Saturday that her prayers remained with victims and survivors the attacks, and paid tribute to the communities that joined together to rebuild after the devastation.
"My thoughts and prayers — and those of my family and the entire nation — remain with the victims, survivors and families affected, as well as the first responders and rescue workers called to duty," she said in a message to U.S. President Joe Biden.
"My visit to the site of the World Trade Center in 2010 is held fast in my memory," she said. Sixty-seven British nationals were among the dead.
The lyrics to the anthem, the Star Spangled Banner, refer to a battle during the War of 1812 between Britain and the fledgling United States. The musical melody evolved from an 18th-century British song.