millions of other Americans, President Barack Obama and first lady Michelle Obama are observing the 10th anniversary of the September 11, 2001 terrorist attacks.
The Obamas are attending events honoring the memory of the nearly 3,000 people killed in and by hijacked aircraft at the former World Trade Center in New York City, in Pennsylvania, and at the Pentagon.
Bells tolled marking the precise moments of the attacks. Family members read names of loved ones who perished.
Peter Negron, who is 22, spoke about his father who died on the 88th floor of the World Trade Center.
"I have stopped crying, but I have not stopped missing my Dad," he said.
President Obama and former president George W. Bush stood together in the new memorial plaza where names of 9/11 victims are inscribed.
The president read a Bible portion chosen for what it said about persevering through difficult challenges.
"We will not fear, even though the Earth be removed, though the mountains be carried into the midst of the sea," he said.
Later, the president laid a wreath at the new 9/11 memorial in Shanksville, Pennsylvania.
The Obamas also walked to a boulder in a field marking the point where United Flight 93, its passengers battling hijackers, hit the ground.
Later the president lays a wreath at the Pentagon, where terrorists steered American Airlines Flight 77 into the building 10 years ago..