The U.S. on Friday will mark the 14th remembrance of the Sept.11, 2001 attacks with ceremonies including memorial services at some sites of the attacks.
One of the memorial services would be at the newly opened Visitor Centre at the rural Pennsylvania site where one of four hijacked airliners crashed.
Similarly moments of silence will be held nationwide to commemorate the deadliest terrorist attacks ever on US soil, which killed 2,977 people.
On September 11, 2001, extremists on suicide missions hijacked four passenger jets, turning the aircraft into guided missiles against the two World Trade Center towers in New York and the Pentagon defence headquarters outside Washington.
A new memorial, which opened Thursday, honours the victims of United Airlines flight 93, the fourth plane seized in the plot, which passengers apparently crashed on a field in Pennsylvania to thwart an attack on Washington.
The Flight 93 National Memorial Visitor Centre, located just outside Shanksville, Pennsylvania, pays tribute to the 40 passengers and crew who died at the site, which is also the final resting place of the victims.
In New York, a ceremony is planned at the National September 11 Memorial and Museum, where family members will read the names of victims of the 2001 attacks and those killed in the 1993 terrorist bombing at the World Trade Center.
In Washington, services will be held for victims’ families at the Pentagon Memorial.