Celebrities are sharing their words and memories about the Sept. 11, 2001 attacks.

17 years ago, in a coordinated terrorist attack, hijackers flew two planes into the World Trade Center and a third into the Pentagon. Passengers on a fourth flight attempted to regain control of a third plane (believed to be headed for the U.S. Capitol) and crashed it into a field in Shanksville, Pennsylvania. That day, nearly 3,000 people died at the three sites and thousands more were injured. In the years since, more than 2,000 people have died from 9/11-related illnesses, sparked by prolonged exposure to toxins at Ground Zero.

On Tuesday, actors, musicians and other stars used their Twitter accounts to remember the tragic events and honor those who died, including rapper and "Law & Order: SVU" star Ice-T, a New Jersey native who says he witnessed the scene from his apartment window.

"It’s 9/11... I actually saw the Towers fall from my apartment window that morning.... Respect to all the victims and people who lost loved ones..." he tweeted Tuesday.

Actor Billy Baldwin honored the "fallen heroes."

"Taking a break today on Twitter to honor all of the fallen heroes of 9/11," he wrote. "Thank you FDNY & NYPD... #NewYorksBravest #NewYorksFinest #NeverForget"

"Shark Tank" star Barbara Corcoran also shared her thoughts: "Everyone remembers 9/11, a day of enormous loss and utter disbelief. I still meet New Yorkers in the neighborhood who lost a father, mother, son or daughter, and I can’t imagine how they found the courage to move past such a personal loss."

"I love you, New York City," Jimmy Fallon wrote.

Charlie Puth shared a photo of his diary entry from the day of the attacks.

"17 years ago today I wrote this in my diary when I was in 4th grade," he tweeted.

Smokey Robinson tweeted, "Remembering the victims and heroes of the attacks on #September11th."

Yoko Ono sent a message signed with love, which she attributed to her and late husband, John Lennon.

Borrowing words from his song "Imagine," she tweeted "Imagine all the people living life in peace."

"Sex and the City" star-turned-politico Cynthia Nixon shared a lengthy message Tuesday.

"On #September11th, I rushed to Sam’s school to make sure he was safe. Then I went to give blood but was turned away because so many had already donated," she tweeted. "On this horrific day, we stood up and came together. I honor those we lost and the heroes who risked their lives."

"Blue Bloods" actress Bridget Moynahan said she's "starting the morning off with a prayer."

Actor and comedian John Fugelsang made a point about the attackers themselves (the vast majority of which were Saudi nationals), tweeting, "Seventeen years ago today America was attacked by zero Afghans, zero Iranians and zero Iraqis."

Pastor-turned-author John Pavlovitz talked about the attacks in a series of tweets.

"As we woke up and went to work and got the kids off to school or got in our cars, September 11th, 2001 was just another day to us – until it wasn't," he tweeted. "We learned to cherish life that day; to love people well, to live with gratitude, to see the best in others, to care for one another as our own. May we not need another horrible day to do that again, America."

Kaya Jones of the Pussycat Dolls shared a video and a message about the attacks.

"#neverforget 911," she wrote. "We love you and we will never forget. May God rest your souls."

Actor Dean Cain ("Lois & Clark: The New Adventures of Superman") simply tweeted a picture of the American flag with the hashtag #Freedom.

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