More than 1,000 people were injured and six killed in the first attack on the World Trade Centre, which rocked the United States 20 years ago on Tuesday.
A ceremony is set to take place in New York honouring those who died. It will be held at the 9/11 memorial at the site where the Twin Towers were hit eight years later, killing more than 2,700 people.
Six Islamist terrorists were convicted of the 1993 bombing from a truck parked in an underground garage below the north tower.
To mark the anniversary, here are some of the most striking images from that tragic day.