Ceremonies at Ground Zero and the Pentagon mark the anniversary of the 9/11 attacks

At the ceremony at Ground Zero in New York, all four living ex-presidents – Joe Biden, George W Bush, Barack Obama and Bill Clinton – are expected to attend.

The current President of the United States, Donald Trump, has announced that he will not attend. The president will instead attend a later ceremony at the Pentagon military headquarters.

A total of seven silent minutes will be observed throughout the day across the United States. One at the time each tower was hit and another when they fell.

A moment of silence will also be observed at the time of the attack on the Pentagon and when Flight 93, where the terrorists were overpowered by passengers, crashed outside of Pennsylvania.

A seventh minute's silence will be observed for all those who died from the health effects of the crime.