Americans mark the 20th anniversary of the 9/11 terror attacks - a series of four coordinated terrorist attacks by the militant group al-Qaeda against the United States of America on the morning of Tuesday, September 11, 2001.
US President Joe Biden has urged Americans to embrace unity as they reflect on the day that two decades ago reshaped the nation.
On that morning, four commercial airliners traveling from the northeastern United States to California were hijacked mid-flight by 19 al-Qaeda terrorists. The hijackers were organized into three groups of five hijackers and one group of four. Each group had one hijacker who had received flight training and took over control of the aircraft.
Al-Qaeda terror group was led by Osama bin Laden who initially denied any involvement in the 9/11 attacks but, in 2004 he formally claimed responsibility for the attacks.