Twenty-five years after the September 11, 2001, terrorist attacks, the United States is commemorating the victims on Friday.
US President Donald Trump is expected to attend a memorial service at the Pentagon, one of the buildings that planes commandeered by terrorists deliberately plunged into, alongside the Twin Towers in New York City.
In New York, relatives are due to read out the names of those killed at the site of the attack on the World Trade Center.
Nearly 3,000 people lost their lives in the terrorist attacks by the al-Qaeda terrorists who hijacked four passenger planes, flying two into the World Trade Center towers and one into the Pentagon, where the Defense Department is based. The fourth crashed in Pennsylvania after passengers on board tackled the hijackers. The hijackers' intended target for the fourth aircraft remains unclear a quarter of a century on.
After the attacks, thousands of people rushed to the site to help search for survivors beneath the rubble.
During Friday's ceremony in New York, attendees are set to observe several moments of silence, as the commemorations also include victims who died later as a result of the attacks.
The US government has acknowledged that the number of people who died from health problems resulting from the attacks has already far exceeded the number killed in the attacks themselves.
So far, the US Centers for Disease Control and Prevention (CDC) has recorded more than 57,000 cases of cancer linked to the attacks.
The collapse of the roughly 400-metre-high towers and the fires that followed released a highly toxic mixture of dust, glass fibres, asbestos, pulverized concrete, plasterboard, burnt plastics and other pollutants into the air, leaving the area hazardous for weeks afterwards.