President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE and other Washington leaders on Tuesday will mark the 17th anniversary of the terrorist attacks of Sept. 11, 2001, during ceremonies and memorials across the country.

Trump will take part in a morning ceremony at the 9/11 memorial in Shanksville, Pa., where United Airlines Flight 93 crash-landed after a group of passengers thwarted a likely attack on the nation's capital. Forty passengers and crew members died as a result of the crash.

First lady Melania Trump Melania TrumpMelania Trump: Ginsburg's 'spirit will live on in all she has inspired' The Hill's 12:30 Report - Presented by Facebook - You might want to download TikTok now Warning label added to Trump tweet over potential mail-in voting disinformation MORE will join the president at Tuesday's event.

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Nearly 3,000 people were killed on Sept. 11, 2001, when hijackers flew commercial airplanes into the World Trade Center towers, the Pentagon and a field in Shanksville.

Trump will speak in Pennsylvania two days after state and local leaders formally dedicated the Tower of Voices, a memorial at the crash site honoring those aboard Flight 93.

The 93-foot tower includes 40 wind chimes, one for each passenger and crew member who died in the crash.

Tuesday marks the second time Trump has observed the anniversary of 9/11 since taking office. Last year, the president spoke at a memorial at the Pentagon, where he vowed to protect America against future terrorist attacks.

While local memorials and vigils are scheduled for Tuesday in towns and cities across the country, here's a look at what leaders in Washington will be doing to observe the day.

Pence to speak at the Pentagon

Vice President Pence will join Defense Secretary James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE and Joint Chiefs of Staff Vice Chairman Gen. Paul Selva at an observance ceremony at the Pentagon, where 184 people were killed in the attack.

All three men are expected to deliver brief remarks, and an officiant will read off the names of those who died in the attack.

An American flag will be unfurled down the side of the building at sunrise, just before 7 a.m.

The event is intended for family members of the dead and Pentagon staff, and is not open to the public.

Moment of silence on Capitol Hill

Congressional lawmakers are not in session until Wednesday, but there will be a campuswide moment of silence at 8:46 a.m. to observe the anniversary of the terrorist attacks. The moment of silence coincides with the time the first plane struck the World Trade Center.

Nielsen to speak at TSA headquarters

Department of Homeland Security (DHS) Secretary Kirstjen Nielsen Kirstjen Michele NielsenDHS IG won't investigate after watchdog said Wolf, Cuccinelli appointments violated law Appeals court sides with Trump over drawdown of immigrant protections Democrats smell blood with new DHS whistleblower complaint MORE will attend a commemoration event at the Transportation Security Administration's (TSA) headquarters in Virginia.

In addition to Nielsen, TSA Administrator David Pekoske and Norman Mineta, who served as Transportation secretary from 2001-2006, will also speak at the event.

Both the TSA and DHS were established in response to the events of 9/11.

Democratic leaders

Senate Minority Leader Charles Schumer (D-N.Y.) will attend the annual ceremony at the World Trade Center site in New York City.

A total of 2,753 people died at the World Trade Center site on Sept. 11, 2001, after American Airlines Flight 11 and United Airlines Flight 175 were hijacked and crashed into the North and South towers, respectively, resulting in the collapse of both buildings.

House Minority Leader Nancy Pelosi Nancy PelosiPelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare House lawmakers reach deal to avert shutdown Centrist Democrats 'strongly considering' discharge petition on GOP PPP bill MORE (D-Calif.) will take part in a National Day of Service and Remembrance in San Francisco. Pelosi will deliver remarks alongside the city's mayor and the mother of a 9/11 victim.

She will then join attendees to pack meals as part of an annual service project associated with the anniversary of the terrorist attacks.

Jordain Carney contributed