In New York City, the crowd gathered near the impressive Manhattan Memorial Museum fell quiet several times for minutes of silence, marking the exact moments when the four planes hijacked by Islamic commandos crashed, and the two World Trade Center towers collapsed in a deluge of steel and dust.

In the audience in New York, Vice President Kamala Harris listened to the long list of victims’ names. Joe Biden was attending another ceremony at the Pentagon.

“The grief fades a little with time, but the permanent absence of my father remains just as present,” said the son of Jon Leslie Albert, one of the victims of the attacks, after reading his father’s name.

Another victim’s relative, calling on the political figures present to heal America’s deep divisions, said that “we shouldn’t need another tragedy to unite our nation”.

On 11 September 2001, 2,977 people died in the deadliest attacks committed by the jihadist organization Al-Qaeda.

On the morning of 11 September 2001, two planes hit the two World Trade Center towers in New York, a third ripped open the Pentagon and a fourth, which appeared to be targeting the Capitol or the White House, crashed in a wooded area of Shanksville, Pennsylvania, after a counterattack by the passengers.

All the people on board the four planes died.

President Joe Biden gathered at the Pentagon. Looking solemn, with one hand on his heart, he participated in a wreath-laying ceremony near the building where one of the hijacked planes crashed, killing 184 people.

“I know that for those who have lost someone, 21 years is both an eternity and such a short time,” the Democrat said at the podium in the light rain.

Joe Biden shared a message sent to the American people on 11 September 2001 by Queen Elizabeth II, who died on Thursday, 8 September. The statement said: “Grief is the price of love.”

“The course of American history changed on that day,” the president said.

But he said what did not change was “the character of this nation,” “the sacrifices, the love, the generosity” of which the United States is capable.

“This day is not about the past; it’s about the future,” Biden said, calling on Americans to defend democracy, the guarantor of freedom that terrorists had sought to “bury in fire, smoke and ash.

Jill Biden, First Lady of the United States, participated in a ceremony in Shanksville, Pennsylvania. 9/11 “reminds us that with courage and kindness, we can be a light in this darkness,” she said, adding that the actions of the passengers on Flight 93 saved many lives, including perhaps that of her husband, then a US senator, who was on his way to Capitol Hill that day.

International leaders also paid tribute to the victims of the attack, which left its mark on the world.

“As we remember 9/11 and the innocent lives lost, we also remember the solidarity that bound us together during those dark hours,” tweeted Ukrainian President Volodymyr Zelensky.

Beyond the terrible toll of thousands of deaths and injuries, thousands more died in the years that followed from illnesses caused by the toxic fumes from the collapse of the Twin Towers.