10 deadliest terror attacks of the 21st century

On September 11, 2001, 19 militants associated with the Islamic extremist group al-Qaeda hijacked four passenger planes operated by two major US air carriers and carried out suicide attacks against targets in the United States. Two of the planes were flown into the World Trade Center (WTC) in New York. The attack killed 2,996 people and injured more than 6,000.