President Barack Obama and other top U.S. officials have paid tribute to the approximately 3,000 people who died in the September 11, 2001, attacks on the United States.
Speaking at a ceremony at the Pentagon, which was hit by one of the four hijacked airplanes, Obama remembered those who were killed and praised the strength of those who suffered losses and were able to pick themselves up and resume their lives.
"Your loved ones' everlasting place is in America's heart. We pray for you, their families who have known the awful depths of loss and in the quiet moments we spend together and from the stories that you've shared I am amazed at will that you've summoned in your lives to lift yourselves up, and to carry on, and to live, and love, and laugh again," Obama said.
"Even more than memorials of stone and water your lives are the greatest tribute to those that we lost, for their legacy shines on in you."
Defense Secretary Chuck Hagel also recalled the losses at the Pentagon that day. "Today we come together in honor of the fallen, surrounded by those who love them," he said.
"We remember each of those taken from us. We remember them as individuals with their own story. We comfort the loved ones they left behind who still mourn and grieve despite the passage of time."
The head of the U.S. Joint Chiefs of Staff, General Martin Dempsey, sounded a note of defiance, saying terrorism could not destroy the values that citizens of the United States embrace.
"No acts of terrorism can strike who we are; nothing can steal away that for which we stand," Dempsey said.
"So today, as we remember the 184 lives that ended here, the many who were injured and all who perished in New York and Somerset County, [Pennsylvania], let us hold firmly to those values for which they believed and for which they lived -- the best of America -- its freedom, its responsibility, and its promise."
PHOTO GALLERY: 'Survivors' Stairs' And Other Mementos Of September 11
A ceremony was also held in New York at the site where the twin towers of the World Trade Center once stood. Bells tolled and the names of the people who were killed were read aloud, in what has become a tradition on the anniversary of the attacks.
A similar ceremony was held at Shanksville, Pennsylvania, where one of the planes crashed, apparently after passengers overpowered the hijackers.
The United States ascertained Osama bin Laden and his Al-Qaeda terrorist network, at the time headquartered in Afghanistan, was to blame for the attacks.
The U.S. and allies launched an attack on Afghanistan before the end of 2001 that drove the Taliban from power but marked the start of war on insurgents that continues to this day.
Bin Laden was killed in Pakistan in 2011 by an elite U.S. commando team.
With reporting by Reuters, AFP, and AP