President Barack Obama has marked the 11th anniversary of the 9/11 attacks, saying the US emerged "even stronger" from that day's death and horror.
In New York, relatives are reading out the names of those killed when hijacked jets were crashed at the World Trade Center, Washington and Pennsylvania.
Mr Obama laid a wreath at the Pentagon and Vice-President Joe Biden is expected to speak at Shanksville. For the first time, politicians will not address the ceremony in New York.
At the Pentagon, Mr Obama addressed survivors of the attacks and relatives of those killed. He told them their loved ones would never be forgotten, and that the dead had "helped us make the America we are today". "The true legacy of 9/11 will not be one of fear or hate or division," Mr Obama said.
"It will be a safer world, a stronger nation, and a people more united than ever before." The National September 11 Memorial and Museum announced in July that this year's ceremony at Ground Zero would include only relatives reading victims' names.
Memorial President Joe Daniels said that, in an election year, it was "honouring the victims and their families in a way free of politics".
Charles Wolf, whose wife Katherine was killed at the World Trade Center, said the absence of elected officials would make the event more intimate for the families.
"We've gone past that deep, collective public grief," he said.
'Time to reflect
Tuesday dawned with a clear blue sky over Washington and New York, jogging memories of a similar September morning 11 years ago.
Nearly 3,000 people were killed that day in attacks by al-Qaeda members who had hijacked four airliners.
President Obama and First Lady Michelle Obama observed a moment of silence at the White House at 08:45 (12:45 GMT).
They then headed to the Pentagon to attend a memorial ceremony there, where one of the jets crashed, and then visit wounded soldiers at Walter Reed Army Medical Center.
With a US election looming in November, President Obama and his Republican rival Mitt Romney have set aside campaigning for the day and will not run negative advertisements.
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