Loved ones of the nearly 3,000 people killed will take part in ceremonies, volunteer work and other tributes honouring the victims.
Americans are marking 24 years since the September 11 attacks with solemn ceremonies, volunteer work and other tributes honouring the victims.
Many loved ones of the nearly 3,000 people killed will join dignitaries and politicians at commemorations on Thursday in New York, at the Pentagon and in Shanksville, Pennsylvania.
