Americans on Tuesday are marking the 17th anniversary of the Sept. 11, 2001 terrorist attacks that killed almost 3,000 people in New York, Virginia and Pennsylvania.
President Donald Trump is attending a ceremony at the 9/11 memorial in Shanksville, Pennsylvania, near where United Airlines Flight 93 crashed after passengers retook control from the al-Qaida-affiliated terrorists who had hijacked the plane.
In the annual presidential proclamation declaring September 11 as Patriot Day, Trump said the "evil acts" did not crush the country's spirit or its commitment to freedom.
Just outside Washington, Vice President Mike Pence is attending a ceremony at the Pentagon.
And in New York, hundreds of survivors and family members of those killed gathered at Ground Zero.
The hijackings were carried out by 19 men affiliated with al-Qaida. The deadliest attack on American soil since Pearl Harbor in 1941, the events of Sept. 11 permanently changed America's perception of security and prompted then-President George W. Bush to declare war on terrorism.