U.S. Vice President Mike Pence (C) speaks during a ceremony marking the 17th anniversary of the Sept. 11 attacks at the Pentagon in Arlington, Virginia, the United States, on Sept. 11, 2018. Memorials were held across the United States on Tuesday to mark the 17th anniversary of the Sept. 11 attacks. (Xinhua/Ting Shen)

Americans commemorated Sept. 11 attacks on Tuesday with solemn memorials in major cities, and a presidential tribute to the victims 17 years after the deadliest terrorist attack on U.S. soil.

In New York City, a traditional commemoration ceremony was held at the site where the World Trade Center's twin towers collapsed, with a moment of silence observed at 8:46 a.m., the exact time the first hijacked airplane struck the North Tower.

The reading of victims' names proceeded with six pauses of silence, each marking a time when the planes hit the two towers and the Pentagon, when another crashed in the state of Pennsylvania, and when the towers crashed.

At the U.S. Department of Defense near Washington D.C., a ceremony featuring U.S. Vice President Mike Pence and Defense Secretary James Mattis began at sunrise with a U.S. flag unfurling on one side of the Pentagon building.

Pence assured family members of the 184 people killed at that site that the nation still grieves with them.

U.S. President Donald Trump visited Shanksville, Pennsylvania, where the fourth airplane hijacked that day crashed after its 40 passengers and crew learned about attacks in New York and Washington and tried to storm the cockpit.

Hundreds of people turned out for the event despite cloudy and chilly weather with a light drizzle, to hear the names of those 40 called along with bell tolls.

Trump hailed the heroism the passengers on United Flight 93 demonstrated when they fought for control of the aircraft after learning the hijackers' intentions, telling their relatives "America will never forget what your loved ones did for all of us."

On the U.S. West Coast, memorial tributes were held across Southern California to commemorate the 17th anniversary of 9/11.

Los Angeles Mayor Eric Garcetti attended an annual remembrance ceremony at the Frank Hotchkin Memorial Training Center of Los Angeles Fire Department along with visiting Paris Mayor Anne Hidalgo and hundreds of people.

A piece of metal from the World Trade Center was on display at the Frank Hotchkin Memorial Training Center in a tribute to the 343 New York firefighters who gave their lives 17 years ago.

Garcetti said during the ceremony that the attacks "shook the world" but the terrorists "did not stop us."

In other cities across Southern California, memorial services were held featuring a moment of silence and lowering of flags.

Nearly 4,000 students and staff from Arcadia High School gathered in the morning for a memorial tribute. They are joined by representatives from the U.S. Marine Corps, Army, Arcadia Fire Department, and Arcadia Police Department.

"We have held this tribute for the past several years, and it's a very powerful, emotional history lesson and reminder for our students, many of whom weren't even born when this tragedy happened," said Ryan Foran, Chief Communications Officer of Arcadia Unified School District.

Moreover, Mayor of Houston Sylvester Turner marked the Sept. 11 attacks in a statement.

He said that "it is a day to reflect on the extraordinary bravery of first responders, the unimaginable grief of the victims' families, the fragility of our democracy and the miracle of life itself."

The United Nations Security Council on Tuesday observed a moment of silence for the victims of the 9/11 attacks prior to a meeting on Syria, at the UN headquarters in New York.

The United States came under multiple terrorist attacks on Sept. 11, 2001, after four civilian aircraft were hijacked and steered toward prominent U.S. buildings.

Three of the planes hit their targets in New York and Washington D.C., while the fourth crashed en route to Washington as its passengers battled for control of the aircraft with the hijackers.

The attacks left nearly 3,000 killed or missing and were the largest terrorist attacks on U.S. soil in history.