9/11 terror attacks: The terror attack in 2001 on one of the then iconic sites in New York, the World Trade Centre, shook the United States and had a huge impact globally. 9/11 terror attacks, also called the September 11 attacks, were a series of four coordinated suicide attacks by the terrorist group al-Qaeda. "Nineteen years ago, under clear blue skies, 102 minutes changed our lives forever. On Fri., Sept. 11, we lead the nation and the world in observing the 19th anniversary of the 2001 attacks and ask you to join us in commemorating," 9/11 Memorial & Museum posted on Twitter.
9/11 attacks were one of the worst in history, which killed 3,000 Americans and others from different countries. Over 6,000 people were injured. The 9/11 attacks changed the global approach and strategy towards tackling terrorism and its perpetrators.
9/11 Attacks: 10 Facts
1. Nineteen al-Qaeda terrorists hijacked four US passenger planes between 8 and 9 am
2. Two of the planes crashed into the Twin Towers of the World Trade Center complex in Manhattan
3. The third plane crashed into the Pentagon, the building that houses the headquarters of the US Department of Defense, in Virginia
4. The fourth plane crashed into a field in Pennsylvania after passengers tried to fight back
5. Within two hours, the two 110-storey towers at the World Trade Centre collapsed. The debris of the Twin Towers led to the collapse of other buildings in the complex
6. The clean-up of the World Trade Center site was completed in May 2002 and the Pentagon building was repaired within a year
7. The investigation into the 9/11 attacks - code-named "PENTTBOM" - was the FBI's largest investigation ever
8. More than half of the agents in FBI worked to identify the attackers and their supporters
9. It included over half-a-million investigative leads, including several hundred thousand tips from the public
10. The crash sites were also the largest crime scenes in FBI history
Several memorials have been built to remember the victims of September 11 attacks. These include the National September 11 Memorial and Museum in New York City, the Flight 93 National Memorial in a field in Stonycreek Township in Pennsylvania and the Pentagon Memorial in Arlington County in Virginia.