Somber scenes of remembrance at 9/11 memorials

A U.S. flag is unfurled at sunrise on Sept. 11, 2018 at the Pentagon on the 17th anniversary of the terror attacks.

Members of the New York City Fire Department stand outside Engine 10 and Ladder 10 firehouse for a moment of silence during observances at the annual ceremony at the Ground Zero memorial site in New York.

Construction worker Nicky Almer plays taps across from the World Trade Center site in New York during a morning commemoration ceremony for victims.

Two members of the New York City fire department look towards One World Trade Center through the open ceiling of the Oculus in New York.

The World Trade Center transit hub known as the Oculus was designed by architect Santiago Calatrava and opened in 2016.

People pause at the north pool of the 9/11 Memorial during ceremonies in New York.

Retired New York City firefighter Bruce Stanley holds a portrait of his late friend and colleague Liam Smith Jr. who died in the attacks, during the commemoration ceremony in New York.

A man wipes a tear while pausing by the south pool of the 9/11 Memorial during ceremonies in New York.

From left, New York Mayor Bill de Blasio, from left, Nikki Haley, the U.S. Ambassador to the United Nations, Rudy Giuliani, lawyer for President Donald Trump and former mayor of New York, and Chris Christie, former governor of New Jersey, attend the ceremony in New York.

Mourners embrace in New York.

White House Chief of Staff John Kelly, center, joins members of the White House staff in observing a moment of silence on the South Lawn of the White House.

The 93-foot tower at the Flight 93 National Memorial is seen from one of the U.S. Marine helicopters transporting President Donald Trump, White House staff and press near Shanksville, Pennsylvania.

President Donald Trump and first lady Melania Trump stand at the memorial in Shanksville.

Attendees waves flags during the memorial service in Shanksville.

Members of the U.S. Naval Academy Glee Club prepare to perform for the remembrance ceremony at the National 9/11 Pentagon Memorial in Arlington, Virginia.

Vice President Mike Pence and Karen Pence attend a wreath-laying ceremony at the Pentagon. They are joined by Vice Chairman of the Joint Chiefs General Paul J. Selva, and Defense Secretary James Mattis, far right.

A guest stands among names at the edge of the north reflecting pool at the National 9/11 Memorial and Museum in New York.

The "Tribute in Light" shines over lower Manhattan near One World Trade Center. The tribute at the site of the fallen World Trade Center towers has been an annual event in New York since 2002.