Relatives of people who died on 9/11 have read out victims’ names, as America 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 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 08:46 – the exact moment the first plane hit the North Tower of the World Trade Center in 2001.
All morning, 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 just outside Washington DC, when the fourth plane crashed in Pennsylvania, and finally when each tower collapsed.
The tributes will continue into the night, when two beams of light will shine 4 miles into the sky where the towers stood.
With thousands of names to read out, the list took hours to get through.
At the memorial in New York, President Joe Biden and First Lady Jill Biden were joined by former Presidents Bill Clinton and Barack Obama, as well as former First Ladies Hillary Clinton and Michelle Obama.
President Biden traveled to all three attack sites on September 11 – New York, Pennsylvania and Virginia.
In a video released on the eve of the anniversary, he paid tribute to the victims.
“No matter how much time has passed, these commemorations bring everything painfully back as if you just got the news a few seconds ago,” the president said.
VP Kamala Harris spoke in Shanksville, Pennsylvania after George W. Bush.
“We must challenge ourselves to look back, to remember, for the sake of our children… and for that reason, we must also look forward,” she said.
In the morning, former President Donald Trump released a video statement, praising first responders – and adding it was a “sad time for the way our war on those that did such harm to our country ended last week” – referring to the US withdrawal from Afghanistan.
However, Donald Trump planned to take part in something quite different later in the day – providing commentary for a boxing match in Florida with his eldest son, Donald Jr.
Other ceremonies included a vigil at the New York Fire Department’s memorial wall – a 56-foot bronze wall that honors the 343 firefighters who died on the day of the attacks.
In total, 441 first responders were killed, the largest loss of emergency personnel in US history.
At the Pentagon outside Washington, a dawn service was held.
Two pipers played Amazing Grace as a small group of military leaders looked on in solemnity, the building bathed in blue light.
A chapel of remembrance now marks the spot where American Airlines flight 77 crashed into the US defense building.