Sept. 11 (UPI) -- New York City, Washington, D.C., and the rest of the United States remembered the Sept. 11, 2001, terrorist attacks Wednesday, the 18th anniversary of the brazen al-Qaida plot that killed 3,000 people at the World Trade Center and Pentagon.
Victims' relatives gathered at Ground Zero in Lower Manhattan Wednesday morning, where the names of the World Trade Center victims were read. A pair of relatives read a series of names, finishing each with a personal tribute. The ceremony included several victims' grandchildren.
Moments of silence and tolling bells marked the exact times when American Airlines Flight 11 (8:46 a.m.) and United Airlines Flight 175 (9:03 a.m.) flew into the twin towers. They also marked the collapses of the skyscrapers roughly an hour later, at 9:59 and 10:28 a.m.
In Arlington, Va., the moment American Airlines Flight 77 crashed into the Pentagon was recognized at 9:37 a.m.
Speaking in front of the Pentagon, President Donald Trump said he remembers watching a business news show that morning that abruptly cut away to scenes of chaos in Lower Manhattan -- and looking from a window in a nearby office tower to see the second plane hit the north tower.
"It was then that I realized that the world was going to change," Trump said.
He recalled going to Ground Zero with several employees to help "in any way that we could."
For the families of the victims, Trump said, that day is etched in their minds with the "last kiss, the last phone call, the last time hearing those precious words, 'I love you.'
"You waited, you prayed, you answered that most dreaded call. And your life changed forever. To each of you, the first lady and I are united with you in grief. We come here in the knowledge that we cannot erase the pain or erase the evil of that dark and wretched day."
Chairman of the Joint Chiefs of Staff Gen. Joseph Dunford Jr. said at the event Wednesday the terrorists failed in their mission.
"The terrorist attacks were intended to challenge our way of life and they sought to break our spirit," Dunford said. "But their purpose was never realized. That day made us stronger and more determined to protect our nation and that with which it stands."
The fight against terrorism began almost immediately in Afghanistan, where U.S. troops remain to this day. Some of the servicemen and women in the armed forces now weren't even alive on Sept. 11. U.S. officials have met with Taliban negotiators in recent months to try and reach a peace agreement that would fully withdraw all American troops. Trump canceled more talks set for last week, after a deadly Taliban attack in Kabul, which killed a U.S. soldier, and criticism of his hosting Taliban officials in the United States so close to Sept. 11.
"Over the last four days, we have hit our enemy harder than they have ever been hit before and that will continue," Trump said. "If for any reason they come back to our country, we will go wherever they are and use power the likes of which the United States has never used before. And I'm not even talking about nuclear power. They will have never seen anything like what will happen to them.
"We do not seek conflict but if anybody dares to strike our land we will respond with the full measure of American power and the iron will of the American spirit," he added. "And that spirit is unbreakable."
Defense Secretary Mark Esper said the terrorists tried to dim the beacon of freedom and hope the United States represents.
"They stole the lives of thousands of innocent people," he said in front of the Pentagon. "While the terrorist attacks brought great pain, the American people responded with even greater bravery and determination.
"A number of you were present in this very building when Flight 77 crashed through its concrete walls."
Former President George W. Bush, who took office less than nine months before the attacks, participated in a wreath-laying ceremony at the Pentagon in the afternoon.
"Terrorist attacks can shake the foundations of our biggest buildings, but they cannot touch the foundation of America," Bush wrote in a Facebook post.
Forty people also died aboard United Airlines Flight 93 when it crashed in a field near Pittsburgh. Vice President Mike Pence visited the site in Shanksville, Pa., Wednesday and spoke about each passenger aboard the hijacked jetliner, praising them for revolting and possibly keeping the plane from hitting another target in Washington, D.C., which most experts believe was the U.S. Capitol.
"It is September 11th again, and it is deeply humbling," Pence said.
"President Trump asked me to be here today to pay a debt of honor to the memory and the families of the 40 passengers and crew members of Flight 93 -- men and women who rose up, who fought back, and who met unspeakable evil with selfless heroism and American strength."
Wednesday night, there was a lighted tribute to the World Trade Center -- the "Tribute in Light," which first appeared in 2002, six months after the attacks.
Although 2,977 victims are listed as having died in the attacks, dozens more have been added in the 18 years since -- firefighters and police who responded and later became terminally ill from working amid the debris of the destroyed towers.
Nearly two-thirds of the World Trade Center responders have at least one certified health condition related to the attack. Comedian and victims' advocate Jon Stewart pushed Congress this year to pass the Victims Compensation Fund.
"We're at 204 in just the [Fire Department of New York] alone, and the [New York City Police Department is] at 241. So I mean, the number of first responders that have died post-9/11 is greater," said Bobby Eustace of the Uniformed Firefighters Association.