New York honoured the nearly 3,000 people killed on September 11, 2001 in a ceremony on Tuesday at Ground Zero, the site where planes hijacked by al-Qaeda brought down the Twin Towers.
The 17th anniversary was commemorated in fog and gentle rain by relatives of those who were killed, police officers, fire fighters and officials, who remembered what remains the deadliest single attack on US soil.
They gathered at the National September 11 Memorial and marked moments of silence at 8:46 am and 9:03 am, the times that the passenger jets struck the North and South Towers.
New York state governor Andrew Cuomo, US ambassador to the United Nations Nikki Haley and the city's mayor, Bill de Blasio, together with his predecessors Michael Bloomberg and Rudy Giuliani, were among those who attended.
"It is not a day to give speeches, it is not a day to talk about politics. It's about the heart," said Alice Greenwald, director of the 9/11 Memorial Museum. "We need to stand together, that's the only way we can deal with that kind of pain."
In what has become an annual tradition, relatives began reading out the long list of those who were killed, saying a few words about those who died, in a ceremony that took longer than three hours.
The New York Stock Exchange also marked a moment of silence at 9:20am and fire stations welcomed relatives of those who were killed. The department suffered a particularly heavy blow, with a total of 343 dead.
In addition to those killed on September 11, thousands of first-responders, construction workers and residents have since developed illness, many of them terminal, as a result of inhaling the toxic fumes.
Al-Qaeda hijacked a total of four planes. The third hit the Pentagon and the fourth, Flight 93, crashed in a field in Shanksville, Pennsylvania.