Kathmandu, 11 September: Today marks the 21st anniversary of the September 11th attacks on the New York-based World Trade Center (WTC)and the Pentagon, and the crash of United Airlines Flight 93.

The 9/11 attacks were carried out by a total of nineteen Arab terrorists from different countries all of them belonging to the al-Qaeda terror group. They hijacked four commercial aeroplanes and after taking control of the aircrafts, the terrorists deliberately crashed two of them into the upper floors of the Twin Towers or the North and South towers of the World Trade Center complex.

The first two crashes occurred in quick succession with the second plane, Flight 175, colliding with the South Tower 17 minutes after Flight 11 crashed into the North Tower. At the time of the attack, there were roughly 16,400 to 18,000 people inside the WTC complex. While most of the people were safely evacuated from the complex, a total of 2,753 people died in New York that day.

Both the buildings caught fire as a result of the crash and the fire was intensified due to the jet fuel of the aircraft. This caused the steel supporting the building structure to melt and weaken and resulted in the collapse of the towers.