Relatives of people who died on 9/11 have read out victims' names, as the US marks 20 years since the deadliest terror attacks on its soil.
Many struggled to hold back tears at the ceremony held at Ground Zero, the site of the Twin Towers destroyed in the attacks by al-Qaeda militants.
A minute's silence was held at the exact time each hijacked plane crashed.
George W Bush, who was the US president at the time, gave a speech in Pennsylvania, where one of the planes crashed into a field after passengers overpowered the hijackers.
The official memorial started with a minute's silence at the exact moment the first plane hit the North Tower of the World Trade Center in 2001.
All day, roses continued to be placed beside the names of the 2,977 victims etched into the Ground Zero memorial.
There were five more moments of silence over the next few hours - marking the time when the second plane crashed into the South Tower, when a third jet struck the Pentagon in Virginia, when the fourth plane crashed in Pennsylvania, and finally when each tower collapsed.
