US Ambassador to Armenia Lynne Tracy and members of the Embassy’s Armenian and American staff gathered at the Embassy’s 9/11 memorial site to observe a moment of silence in honor of those who were killed or injured in the attacks 20 years ago.
On Tuesday 11 September 2001 suicide attackers seized US passenger jets and crashed them into two New York skyscrapers, killing thousands of people.
The attack remains one of the most traumatic events of the century, not only for Americans but also for the world.
Four planes flying over the eastern US were seized simultaneously by small teams of hijackers.
They were then used as giant, guided missiles to crash into landmark buildings in New York and Washington.
Two planes struck the Twin Towers of the World Trade Center in New York.
The first hit the North Tower at 08:46 Eastern Time (13:46 GMT). The second crashed into the South Tower at 09:03.
The buildings were set on fire, trapping people on the upper floors, and wreathing the city in smoke. In less than two hours, both 110-storey towers collapsed in massive clouds of dust.
At 09:37 the third plane destroyed the western face of the Pentagon – the giant headquarters of the US military just outside the nation’s capital, Washington DC.
The fourth plane crashed in a field in Pennsylvania at 10:03 after passengers fought back. It is thought the hijackers had meant to attack the Capitol Building in Washington DC.