President Donald Trump is marking 17 years since the September 11 terror attack by visiting a Pennsylvania field that became a memorial.
Trump and his wife Melania are to participate in Tuesday's remembrance event in Shanksville, where hijackers crashed a California-bound commercial airliner on September 11, 2001, after the 40 passengers and crew members learned what was happening and attempted to regain control of the aircraft. Everyone on board was killed.
Nearly 3,000 people died on 9/11 when other airplanes were flown into New York's World Trade Centre and the Pentagon in an attack planned by al-Qaeda leader Osama bin Laden.
The Flight 93 memorial in Shanksville, Pennsylvania. Image: Getty
Bin Laden was killed in 2011 during a military operation ordered by then-president Barack Obama.
"Certainly the focus will be on remembering that horrific day and remembering the lives that were lost, and certainly honouring the individuals who were not only lost that day, but also put their lives of the line to help in that process," White House press secretary Sarah Huckabee Sanders said.
Trump observed the anniversary for the first time as president last year. He his wife led a moment of silence at the White House accompanied by aides and administration officials at the exact time that hijackers flew the first of two airplanes into the World Trade Centre's Twin Towers.
The president also participated in the Pentagon's September 11 observance last year. Vice President Mike Pence will represent the administration there on Tuesday.