Spontaneous celebrations broke out in a number of cities late Sunday night as the world learned that the mastermind of the worst terrorist attack on American soil is dead. Almost 10 years after the attacks that killed more than 3,000 people, President Obama announced late Sunday night that Osama bin Laden was killed by U.S. special forces in Pakistan.

Hundreds of people arrived at the White House late Sunday night and chanted, "USA! USA!" for hours. Large crowds also gathered in celebration in New York's Time Square and at Ground Zero well after midnight.

Internet users turned to Twitter and Facebook to post celebratory messages from across the globe.

"The death of bin Laden marks the most significant achievement to date in our nations effort to defeat Al Qaeda," Obama said in a dramatic late-night televised address that was watched around the world.

On the Internet: "Bin Laden is finally&.dead! I'm the happiest arab on the planet!"
-- Tweet by @randajarrar via the Wall Street Journal

The President's announcement: "On nights like this one we can say to those families who have lost loved ones to al Qaedas terror: Justice has been done."
-- President Obama

9/11 survivors and families: "It cannot ease our pain, or bring back our loved ones. It does bring a measure of comfort that the mastermind of the September 11th tragedy and the face of global terror can no longer spread his evil."
-- Gordon Felt,
President of the Families of Flight 93