The September 11 attacks were carried out by members of al-Qaeda.
Two weeks after the September 11 attacks , the Federal Bureau of Investigation connected the hijackers to al-Qaeda , a global , decentralized terrorist network . September 11 attacks . were a series of four coordinated terrorist attacks by the Islamic terrorist group al-Qaeda on the United States on the morning of Tuesday , September 11 , 2001 . Four passenger airliners operated by two major U.S. passenger air carriers ( United Airlines and American Airlines ) -- all of which departed from airports in the northeastern United States bound for California -- were hijacked by 19 al-Qaeda terrorists . Although al-Qaeda 's leader , Osama bin Laden , initially denied any involvement , in 2004 he claimed responsibility for the attacks .