Commemoration events have been held in the US to mark the eighth anniversary of the 9/11 terror attacks on New York, the Pentagon and Pennsylvania.
In New York, friends and relatives of those who died in the attacks on the World Trade Center gathered at Ground Zero.
They placed flowers in the reflecting pool where the towers once stood and the names of each of the more than 2,700 victims were read out.
An American flag which was found in the ruins of the collapsed buildings was carried through the event by New York firefighters.
President Barack Obama and his wife Michelle joined White House staff in observing a minute's silence.
Mr Obama also laid a wreath at the US military headquarters at the Pentagon, where 184 people were killed when a plane was flown into the building.
In pouring rain, the president met relatives of Pentagon staff who died. He said nothing would "diminish the pain and the loss of that day".
In Shanksville, Pennsylvania, friends and relatives of victims held a commemorative flag to those on board United Flight 93, which crashed in a field as passengers and crew tried to wrest control of the plane from hijackers.
The day was also marked in Afghanistan, where ceremonies were held by soldiers fighting the war which followed the attacks.
Many people are angry that despite redevelopment and memorial plans, Ground Zero remains a building site eight years after the attacks.
There was a brief security scare in Washington when it was reported that shots had been fired at a boat acting suspiciously on the Potomac River, but it was later confirmed to have been a training exercise.
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