S President Joe Biden has called for unity as the country remembers the victims of the September 11 2001 attacks.
A third plane smashed into the Pentagon, just outside Washington DC and a fourth plane crash landed in a field in Pennsylvania after passengers fought back against the terrorists.
“We honour all those who risked and gave their lives in the minutes, hours, months and years afterwards,” Mr Biden said.
“No matter how much time has passed, these commemorations bring everything painfully back as if you just got the news a few seconds ago.”
In his statement, President Biden said there were “darker forces of human nature – fear and anger, resentment and violence against Muslim Americans” which followed the attacks.
However, he said the unity had remained the “greatest strength” of the US.
“We learned that unity is the one thing that must never break,” he added.
President Biden and the first lady Jill Biden will visit the three attack sites.
There will also be six moments of silence to correspond with the times the tragedies unfolded.
In the evening, a special light will project two beams into the sky where the towers once stood tall over New York City.
The Department of Defense will also hold a private memorial which will commorate the people killed in Washington, DC on 9/11.
Also, a flag will be showcased on the west side of the building at sunrise in tribute.
Families of the victims of United flight 93 will have a private ceremony at the National Memorial site near Shanksville.
