President Donald Trump led a short ceremony at the White House today to mark the 16th anniversary of the attacks of September 11, 2001.
The American flag was also unfurled on the western side of the Pentagon to mark the attacks on the United States.
Nearly 3,000 people were killed that day when four jetliners were hijacked by militants from al Qaeda.
Two planes crashed into the World Trade Center's twin towers, another hijacked plane ploughed into the Pentagon, and a fourth hijacked plane crashed into a field in Shanksville, Pennsylvania while heading for Washington.