Americans are marking the 17th anniversary of the September 11, 2001, terror attacks with solemn commemorations at the World Trade Center site in New York City, the Pentagon in Washington, D.C., and a field in Pennsylvania.
Thousands of people are participating in the ceremonies, while countless others privately remember the attacks that took nearly 3,000 lives and changed millions more.
In New York, the ceremony at the memorial plaza where the World Trade Center's twin towers once stood began with a moment of silence and tolling bells at 8:46 a.m., the time when the trade center was hit by the first of two passenger jets piloted by terrorist hijackers from Al-Qaeda. Relatives of victims held signs bearing photos of the loved ones they lost.
President Donald Trump and his wife, Melania, traveled to Shanksville, Pennsylvania, where the fourth of the four planes crashed into a field after passengers rushed the cockpit and seized control of the plane from hijackers.
Trump praised the courage of the "heroes" aboard Flight 93, saying, "The passengers and crew members came together, took a vote, and they decided to act."
Vice President Mike Pence spoke at the Pentagon, where one of the planes slammed into the headquarters of the U.S. military.
Nearly 3,000 people died in the September 11 attacks, most of them when the two World Trade Center towers collapsed.
The deadliest terror attack on American soil, it was followed by a U.S.-led invasion of Afghanistan, where war continues years after coalition forces drove the Taliban -- which has harbored Al-Qaeda leaders including Osama bin Laden, who was later killed in a U.S. operation in Pakistan -- from power.
Meanwhile, more than 38,000 people suffered from respiratory and other ailments from the toxic dust that covered much of lower Manhattan when the towers collapsed.
The site of the collapsed towers has been transformed with new soaring skyscrapers rising, a new transportation hub, and a vast museum dedicated to the victims.