A man mourns at the 9/11 Memorial on the 20th anniversary of the September 11 attacks in Manhattan, New York on September 11, 2021

New York (AFP) - America marked the 20th anniversary of 911 Saturday with pleas for unity at solemn ceremonies given added resonance by the messy withdrawal of US troops from Afghanistan and return to power of the Taliban.

At the 911 memorial in New York, relatives wiped away tears, their voices breaking as they read out the names of the almost 3,000 people killed in the Al-Qaeda attacks.

“We love you and we miss you,” many of them said as somber violin music played at the official ceremony, attended by dignitaries including President Joe Biden and former presidents Barack Obama and Bill Clinton.

Twenty years have passed since the 9/11 attacks by Al-Qaeda in the United States, but the fallout remains painful for Americans

The service at the Ground Zero site where 2,753 people died – some of whom jumped to their deaths from the collapsing towers – started shortly after 8:30 am (1230 GMT) under tight security, with Lower Manhattan effectively locked down.

The first of six moments of silence were marked at 8:46 am, with a bell ringing to symbolize the time the first hijacked plane crashed into the North Tower of the World Trade Center.

At 9:03 am, attendees stood still again to mark the moment the South Tower was struck. At 9:37 am, it was the Pentagon, where the hijacked airliner killed 184 people in the plane and on the ground.

New York police and firefighters hold a US flag as a band plays the US National Anthem at the National 9/11 Memorial during a ceremony commemorating the 20th anniversary of the 9/11 attacks on the World Trade Center, in New York, on September 11, 2021

At 9:59, the moment the South Tower fell. At 10:03 am, they remembered the fourth plane to crash in a field in Shanksville, Pennsylvania, after passengers fought the hijackers. And at 10:28 am, the North Tower falling.

Mourners clutched photos of their loved ones, their pain still raw despite a whole generation having grown up since the morning of September 11.

“It feels like it was yesterday. Every year (that) we get further away it becomes more important to remember” Joanne Pocher-Dzama, whose brother died at the World Trade Center, told AFP.

Bruce Springsteen sang I’ll See You in My Dreams” and across New York smaller ceremonies took place at fire stations in remembrance of the 343 firefighters who lost their lives saving others. After nightfall, twin light beams were to projected into the sky.

US President Joe Biden (R), with former President Barack Obama (L), speaks with former First Lady Michelle Obama as they attend the ceremony at the National 9/11 Memorial marking the 20th anniversary of the 9/11 attacks on the World Trade Center, in New York, on September 11, 2021

Heart-wrenching commemorations also took place at the Pentagon and Shanksville, where former president George W. Bush said the unity America showed following the attacks “seems distant” from today.

“So much of our politics has become a naked appeal to anger, fear, and resentment. That leaves us worried about our nation and our future together,” he told mourners.

- ‘Unity’ -

In a video posted on the eve of the anniversary, Biden urged Americans to come together.

“To me, that’s the central lesson of September 11th. It’s that at our most vulnerable, in the push and pull of all that makes us human, in the battle for the soul of America, unity is our greatest strength,” Biden said in a six-minute message from the White House.

This file photo taken on September 11, 2001, shows Edward Fine covering his mouth as he walks through dust and debris following the collapse of one of the twin towers of the World Trade Center

But former president Donald Trump shattered that unity, releasing a video message slamming the “inept administration” of Biden for its “incompetence” over the Afghan withdrawal.

The memorials come less than two weeks since the last soldiers left Kabul airport, ending the so-called “forever war.”

But national discord over the chaotic exit, including the deaths of 13 US troops in a suicide bomb and the return to power of Al-Qaeda founder Osama bin Laden’s protectors the Taliban, has overshadowed what was supposed to be a pivotal day in Biden’s nearly eight-month-old presidency.

In the last 20 years, bin Laden has been hunted down and killed and towering new sky scraper has risen over Manhattan, replacing the Twin Towers, dubbed the “Freedom Tower.”

But the effects of 911 rumble on.

The 'Tribute in Light' public art installation commemorates the 9/11 2001 terrorist attacks that destroyed the Twin Towers

In Guantanamo Bay, accused 911 mastermind Khalid Sheikh Mohammed and four other men continue to await trial, nine years after charges were filed.

And only last week did Biden order the release of classified documents from the FBI investigation over the next six months.

World leaders sent messages of solidarity to the United States, saying the attackers had failed to destroy Western values.

“They failed to drive our nations apart, or cause us to abandon our values, or to live in permanent fear,” said British leader Boris Johnson.