US President Barack Obama has confirmed the death of Osama bin Laden in an historic address from the White House, where thousands of Americans gathered as news spread about the terrorist leader's demise.
Moments after he spoke, American officials cautioned that the events could lead to heightened threats against the United States.
Officials said the US would ensure that bin Laden's body was handled in accordance with Islamic tradition.
Americans welcome the news
Joyous crowds spontaneously erupted with chants of "USA, USA," as news of bin Laden's death was welcomed by ordinary Americans.
Some brandishing US national flags, they punched the air and sang The Star Spangled Banner, even before the announcement of his death by President Barack Obama in a hurriedly-organised address to the nation.
"I'm proud to be an American tonight," Kenneth Specht, a New York firefighter on 9/11, told CNN, paying tribute to the victims of the attacks in New York and Washington.
"Tonight they are first and foremost in our minds," he said.
Terrorist mastermind killed in Pakistan firefight
Bin Laden - head of militant Islamist group Al Qaeda and mastermind of the September 11, 2001, terrorist attacks - was killed in an attack carried out by a small group of US forces last week, President Obama said.
His death was the greatest victory in a decade-long fight to defeat Al Qaeda and prevent more attacks on American soil, President Obama said.
He called bin Laden a mass murderer and a terrorist who killed nearly 3000 Americans, including many Muslims, he said.
"His demise should be welcomed by all who believe in peace and human dignity."
President Obama said the intelligence which led to bin Laden's death was first gathered in August last year.
It led US agents to track bin Laden to a compound "deep within Pakistan", he said.
Last week, he decided there was enough information to order the deadly attack.
The attack had served justice for the "senseless slaughter" of the September 11 terrorist strikes which had left a deep scar across the US, President Obama said.
"Let me say to the families who lost loved ones on 9/11 that we have never forgotten your loss.
"Today's achievement is a testament to the greatness of our country."
Obama's predecessor offers his congratulations
Former US President George W. Bush says he has congratulated President Barack Obama after hearing about the death of Osama bin Laden.
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."
He also said the US "has sent an unmistakable message: No matter how long it takes, justice will be done. "
Fisk: bin Laden's death won't make a difference
A senior U.S. counterterrorism official said bin Laden was killed in a ground operation in Pakistan, not by a Predator drone.
Officials have long believed bin Laden, the most wanted man in the world, was hiding a mountainous region along the Pakistan-Afghanistan border.
He had been hunted by US forces for nearly a decade.
Foreign correspondent for the Independent newspaper, Robert Fisk, who met and interviewed bin Laden three times, told Al Jazeera his death would have little impact on Al Qaeda's operations or on the Arab/Muslim world.
"What he wanted to do he has done and I don't think his death will make a difference."
"I don't really think Al Qaeda needs a leadership and I don't doubt very much bin Laden was still the leader. He was certainly the founder ... but to suggest he was in control of Al Qaeda ... is complete rubbish.
"I think he spend most of his time hiding."
NZ leaders react
Prime Minister John Key said bin Laden was responsible for thousands of deaths, including New Zealanders, around the world.
While it would not necessarily bring "an immediate end to terrorist activity ... I have absolutely no doubt that the world is a safer place".
"For all those who have lost a loved one [in terrorist attacks], they may feel now that some sense of justice has been achieved."
Labour leader Phil Goff, who was giving a press conference when the news came through of bin Laden's death, told the Herald the world was a better place.
"Osama bin Laden is responsible for the deaths of thousands of innocent civilians," said Goff.
"I have absolutely zero tolerance for terrorists who kill innocent people in pursuit of their ideological goals.
"The world is a better place."
- WITH AP, AFP