Americans honour nearly 3,000 people killed on September 11, 2001 in a solemn ceremony at ground zero, where hijacked planes brought down the Twin Towers.
Americans commemorated 9/11 with solemn ceremonies and vows on Wednesday to "never forget" 18 years after the deadliest terror attack on American soil.
Victims' relatives assembled at ground zero, where the observance began with a moment of silence and the tolling of bells at 8:46 am — the moment a hijacked plane slammed into the World Trade Center's north tower.
"As long as the city will gift us this moment, I will be here," Margie Miller, who lost her husband, Joel, said at the ceremony, which she attends every year. "I want people to remember."
After so many years of anniversaries, she has come to know other victims' relatives and to appreciate being with them.
"There are smiles in between the tears that say we didn't do this journey on our own. That we were here for each other. And that's the peace that I think we get from being here," she said.
Moment of silence
President Donald Trump and first lady Melania Trump led a moment of silence on the White House South Lawn and then were expected to join an observance at the Pentagon.
Vice President Mike Pence was scheduled to speak at the third crash site, near Shanksville, Pennsylvania.
Former President George W Bush, commander-in-chief at the time of the 2001 attacks, was due at an afternoon wreath-laying at the Pentagon.
The anniversary ceremonies centre on remembering the nearly 3,000 people killed when hijacked planes slammed into the trade centre, the Pentagon and a field near Shanksville on September 11, 2001.
Afghan peace talks
The nation is still grappling with the aftermath of 9/11. The effects are visible from airport security checkpoints to Afghanistan, where the post-9/11 US invasion has become America's longest war.
Earlier this week, Trump called off a secret meeting at Camp David with Taliban and Afghan government leaders and declared the peace talks "dead."
As the September 11 anniversary began in Afghanistan, a rocket exploded at the US embassy just after midnight.
Trump also used 9/11 remembrance commemorations to announce an unprecedented escalation of the US military assault on Afghanistan's Taliban –– just days after he wanted to hold peace talks with the group.
Speaking at a Pentagon ceremony, Trump said that over "the last four days" US forces have "hit our enemy harder than they have ever been hit before and that will continue."
The precise nature of the US offensive against the Taliban that Trump described was not immediately clear.
All those victims' names are read aloud at the ground zero ceremony by loved ones — now, quite often, ones too young to have known their lost relatives.
"Uncle Joey, I wish I got to know you," Joseph Henry said of his uncle and namesake, firefighter Joseph Patrick Henry. "I know that you're watching over us right now."
Others made a point of spotlighting the suffering of another group of people tied to the tragedy: firefighters, police and others who died or fell ill after exposure to the wreckage and the toxins unleashed in it.
"As we honour and remember all those who died on 9/11 and their families, let us not forget the first responders who have died since 9/11 and their families," Maureen Pulia said after reading names at ground zero. Her cousin Thomas Anthony Casoria, a firefighter, was killed there.
A compensation fund for people with potentially September 11-related health problems has awarded more than $5.5 billion so far. More than 51,000 people have applied.
Over the summer, Congress made sure the fund won't run dry.
The sick gained new recognition this year at the memorial plaza at ground zero, where the new 9/11 Memorial Glade was dedicated this spring.
Sept. 11 has become known also as a day of service. People around the country volunteer at food banks, schools, home-building projects, park cleanups and other charitable endeavors on and near the anniversary.