In ways both subtle and plain, the aftermath of 9/11 ripples through American politics and public life to this day.

9/11 is federally recognised as both Patriot Day and a National Day of Service and Remembrance.
9/11 is federally recognised as both Patriot Day and a National Day of Service and Remembrance. (AP)

Americans are remembering 9/11 with moments of silence, readings of victims' names, volunteer work, candlelight vigils and other tributes 21 years after the deadliest terror attack on US soil.

Victims’ relatives and dignitaries will convene on Sunday at the places where hijacked jets crashed on September 11, 2001 — the World Trade Center in New York, the Pentagon and a field in Pennsylvania.

The attack, conducted by Al Qaeda members who seized control of the jets to use them as missiles, killed nearly 3,000 people and spurred a US "war on terror", which led to the Washington's invasion of Afghanistan, and also affected millions of people worldwide.

It also stirred — for a time — a sense of national pride and unity for many, while subjecting Muslim Americans to years of suspicion and bigotry and engendering debate over the balance between safety and civil liberties.

President Joe Biden plans to speak and lay a wreath at the Pentagon, while first lady Jill Biden is scheduled to speak in Shanksville, Pennsylvania, where one of the hijacked planes went down after passengers and crew members tried to storm the cockpit as the hijackers headed for Washington.

Vice President Kamala Harris and husband Doug Emhoff are due at the National September 11 Memorial in New York, but by tradition, no political figures speak at the ground zero ceremony. It centres instead on victims' relatives reading aloud the names of the dead.

READ MORE: FBI unveils first document linked to 9/11 attacks investigation

'I can never recover'

The attacks have cast a long shadow into the personal lives of thousands of people who survived, responded or lost loved ones, friends and colleagues.

More than 70 of Sekou Siby's co-workers perished at Windows on the World, the restaurant atop the trade centre's north tower. Siby had been scheduled to work that morning until another cook asked him to switch shifts.

Siby never took a restaurant job again; it would have brought back too many memories. The Ivorian immigrant wrestled with how to comprehend such horror in a country where he'd come looking for a better life.

He found it difficult to form the type of close, family-like friendships he and his Windows on the World co-workers had shared.

It was too painful, he had learned, to become attached to people when “you have no control over what’s going to happen to them next.”

“Every 9/11 is a reminder of what I lost that I can never recover,” says Siby, who is now president and CEO of ROC United. The restaurant workers' advocacy group evolved from a relief centre for Windows on the World workers who lost their jobs when the twin towers fell.

Sentiments around September 11 centre around 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.

Some relatives of the victims 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.

READ MORE: 20 years after 9/11, the ‘War on Terror’ has brought the US only defeat

Source: AP