NEW YORK, United States (AP) — Americans remembered 9/11 on Sunday with tear-choked tributes and pleas to “never forget”, 21 years after the deadliest terror attack on US soil.

The loss still feels immediate to Bonita Mentis, who wore a necklace with a photo of her slain sister, Shevonne Mentis.

“It’s been 21 years, but it’s not 21 years for us. It seems like just yesterday,” she said before reading victims’ names at the World Trade Center to a crowd that included Vice-President Kamala Harris and husband Doug Emhoff.

At the Pentagon, which also was targeted on 9/11, President Joe Biden vowed that the US would continue working to root out terrorist plots and called on Americans to stand up for “the very democracy that guarantees the right to freedom that those terrorists on 9/11 sought to bury in the burning fire, smoke and ash”. First lady Jill Biden spoke at the third attack site, a field near Shanksville, Pennsylvania.

On September 11, 2001, conspirators from the al-Qaida Islamic terror group seized control of jets to use them as passenger-filled missiles, hitting the trade centre’s twin towers and the Pentagon. The fourth plane was headed for Washington but crashed near Shanksville after crew members and passengers tried to storm the cockpit.

The attacks killed nearly 3,000 people, reconfigured national security policy and spurred a US “war on terror” worldwide. Sunday’s observances came little more than a month after a US drone strike killed a key al-Qaida figure who helped plot the 9/11 attacks, Ayman al-Zawahri.

Pierre Roldan, who lost his cousin Carlos Lillo, a paramedic, said “we had some form of justice” when a US raid killed Osama bin Laden in 2011.

“Now that al-Zawahri is gone, at least we’re continuing to get that justice,” Roldan said.

The self-proclaimed mastermind of the attacks, Khalid Shaikh Mohammed, still awaits a long-postponed military tribunal. An attorney for one of Mohammed’s co-defendants this week confirmed ongoing negotiations toward a potential agreement to avoid a trial and impose lesser but still lengthy sentences.

The September 11 attacks stirred — for a time — a sense of national pride and unity for many, while also subjecting Muslim Americans to years of suspicion and bigotry and engendering debate over the balance between safety and civil liberties. In ways both subtle and plain, the aftermath of 9/11 ripples through American politics and public life to this day.

But like some other victims’ relatives, Jay Saloman fears that Americans’ consciousness of 9/11 is receding.

“It was a terrorist attack against our country that day. And theoretically, everybody should remember it and, you know, take precautions and watch out,” said Saloman, who lost his brother, Wayne Saloman.

By tradition, no political figures speak at the ground zero ceremony. The observance centres, instead, on relatives reading aloud the names of the dead.

Like a growing number of readers, firefighter Jimmy Riches’ namesake nephew wasn’t born yet when his relative died. But the boy took the podium to honour him.

“You’re always in my heart. And I know you are watching over me,” he said.

Nikita Shah wore a T-shirt that bore the de facto epigraph of the annual commemoration — “never forget” — and the name of her father, Jayesh Shah. She was 10 when he was killed.

The family later moved to Houston but often returns to New York for the anniversary to be “around people who kind of experienced the same type of grief and the same feelings after 9/11,” said Shah.

Readers often add personal remarks that form an alloy of American sentiments about September 11 — grief, anger, toughness, appreciation for first responders and the military, appeals to patriotism, hopes for peace, occasional political barbs, and a poignant accounting of the graduations, weddings, births and daily lives that victims have missed. A few readers note recent events, this year ranging from the still ongoing coronavirus pandemic to Russia’s war in Ukraine.

Some relatives also lament that a nation which came together — to some extent — after the attacks has since splintered apart. So much so that federal law enforcement and intelligence agencies, which were reshaped to focus on international terrorism after 9/11, now see the threat of domestic violent extremism as equally urgent.

“It took a tragedy to unite us. It should not take another tragedy to unite us again,” said Andrew Colabella, whose cousin, John DiGiovanni, died in the 1993 bombing World Trade Center bombing that presaged 9/11.

Beyond the attack sites, communities around the country marked the day with candlelight vigils, interfaith services and other commemorations. Some Americans joined in volunteer projects on a day that is federally recognised as both Patriot Day and a National Day of Service and Remembrance.

Others observed the anniversary with their own reflections.

More than 70 of Sekou Siby’s co-workers perished at Windows on the World, the restaurant atop the trade centre’s north tower. He had the day off because another cook asked him to switch shifts.

The Ivorian immigrant wrestled with how to comprehend such horror in a country where he’d come looking for a better life. And Siby, now president of restaurant workers’ advocacy group ROC United, said ahead of the anniversary that the attacks made him wary of becoming attached to people when “you have no control over what’s going to happen to them next.”

“Every 9/11 is a reminder,” he said, “of what I lost that I can never recover.”