Americans on Wednesday are marking the 18th anniversary of the Sept. 11, 2001 terrorist attacks that killed almost 3,000 people in New York, Virginia and Pennsylvania.
Just outside Washington, President Donald Trump is attending a ceremony at the Pentagon for families of those killed when a hijacked plane crashed into the building.
In New York, hundreds of survivors and family members of those killed will gather at Ground Zero, where the Twin Towers of the World Trade Center stood before two hijacked commercial flights brought them down.
Vice President Mike Pence is due to attend ceremonies 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.
The hijackings were carried out by 19 men affiliated with al-Qaida. The deadliest attack on American soil since Pearl Harbor in 1944, the events of Sept. 11 permanently changed America’s perception of security and prompted then-President George W. Bush to declare war on terrorism and invade Afghanistan.