President Barack Obama on Sunday announced that the U.S. had killed al Qaeda leader Osama bin Laden, accused of being the mastermind behind the 9/11 attacks in 2001.

The death of bin Laden marks the most significant achievement to date in our nation's effort to defeat al Qaeda, Obama said from the East Room of the White House late Sunday.

Justice has been done, he said.

It was nearly 10 years ago that a bright September day was darkened by the worst attack on the American people in our history, Obama said, recalling the attacks that destroyed the World Trade Center in New York city and damaged part of the Pentagon in Washington D.C.

Nearly 3,000 citizens taken from us, leaving a gaping hole in our hearts, he said.

Obama said the U.S. is not - and never will be - at war with Islam.

I've made clear, just as President Bush did shortly after 9/11, that our war is not against Islam. Bin Laden was not a Muslim leader; he was a mass murderer of Muslims. Indeed, al Qaeda has slaughtered scores of Muslims in many countries, including our own. So his demise should be welcomed by all who believe in peace and human dignity, Obama said.

George W. Bush Reacts

Former President George W. Bush, whose administration began a war in Afghanistan in 2002, months after the attacks, said Obama called to inform him of the event.

I congratulated him and the men and women of our military and intelligence communities who devoted their lives to this mission. They have our everlasting gratitude, Bush said.

This momentous achievement marks a victory for America, for people who seek peace around the world, and for all those who lost loved ones on September 11, 2001. The fight against terror goes on, but tonight America has sent an unmistakable message: No matter how long it takes, justice will be done, he said.

Crowds Gather

Reports began showing large crowds gathering outside the White House in Washington D.C. and the World Trade Center in New York City.

New York City Mayor Michael Bloomberg also weighed in.

New Yorkers have waited nearly ten years for this, Bloomberg said.

Pakistani Cooperation

Obama said counterterrorism cooperation with Pakistan helped in the effort against bin Laden.

He said he spoke with Pakistani President Asif Ali Zardari administration's officials had spoken with their Pakistani counterparts.

They agree that this is a good and historic day for both of our nations. And going forward, it is essential that Pakistan continue to join us in the fight against al Qaeda and its affiliates, he said.

The Operation

Tonight, I can report to the American people and to the world that the United Sates has conducted an operation that killed Osama bin Laden, the leader of al Qaeda, and a terrorist who's responsible for the murder of thousands of innocent men, women, and children, Obama said from the White House.

Obama said that when he came into office in January of 2009 he told CEA director Leon Pannetta the killing or capture of bin Laden was the top priority of our war against al Qaeda.

Obama revealed that last August after years of painstaking work by our intelligence community, I was briefed on a possible lead to bin Laden.

It was far from certain, and it took many months to run this thread to ground. I met repeatedly with my national security team as we developed more information about the possibility that we had located bin Laden hiding within a compound deep inside of Pakistan. And finally, last week, I determined that we had enough intelligence to take action, and authorized an operation to get Osama bin Laden and bring him to justice, Obama said.

He said that U.S. on Sunday launched a targeted operation against that compound in Abbottabad, Pakistan.

He said a small team of Americans carried out the operation.

No Americans were harmed. They took care to avoid civilian casualties. After a firefight, they killed Osama bin Laden and took custody of his body, he said