The United States marked the 20th anniversary of the 9/11 attacks with pleas for unity at solemn ceremonies given added resonance by the chaotic withdrawal of US troops from Afghanistan and the return to power of the Taliban.

At the September 11 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 attacks, the deadliest in US history.

The service at “Ground Zero” where most died – some of whom jumped to their deaths from the burning towers of the World Trade Center – took place under tight security, with Lower Manhattan effectively locked down.

The first of six moments of silence was marked at 8:46am, with a bell ringing to symbolise the time the first hijacked plane crashed into the North Tower.

At 9:03am, 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.

At 9:59am, 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 10:28am, the North Tower falling.

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