U.S. President Barrack Obama on Monday praised the work of the country's special forces in killing Osama bin Laden, calling the daring nighttime raid in Pakistan a source of renewed unity.

"I think we experienced the same sense of unity that prevailed on 9/11," Obama said at a White House gathering, praising "the heroes that carried out this incredible mission."

Obama announced late Sunday that the world's most wanted terrorist for almost 10 years had been killed. 

"This is a good day for America," the president said the day after delivering the news.

The White House said Obama would be in New York City on Thursday to mark bin Laden's killing and to honour the victims of the Sept. 11, 2001, attacks on the U.S.

Officials said the mission was months in the planning.

It began with CIA interrogators in secret overseas prisons obtaining critical names and other information.

However, American forces were led to bin Laden by his most trusted courier, a Kuwaiti-born man named Sheikh Abu Ahmed, according to three U.S. officials who spoke on condition of anonymity.

Ahmed was a shadowy figure for U.S. intelligence, someone it took many years to identify. For a long time, intelligence officials knew him only by his nom de guerre, Abu Ahmed al-Kuwaiti. The first indications about his significance came from CIA detainees shortly after the Sept. 11 attacks.

Ahmed and his brother were killed in the same pre-dawn raid Monday that left bin Laden dead.

Once the strong likelihood was established that bin Laden was in the compound, Obama ordered a risky, unilateral mission to capture or kill the al-Qaeda leader on foreign soil. Four helicopters carrying CIA paramilitaries and a U.S. Navy SEAL team swooped into the specially built residence in Abbottabad, about 150 kilometres north of Islamabad.

'Minutes passed like days'

Details began emerging Monday about the tense moments for the president and his advisers as the raid unfolded.

"It was probably one of the most anxiety-filled periods of time, I think, in the lives of the people who were assembled here," John Brennan, the U.S. government's counterterrorism chief, said at a news conference.

"The minutes passed like days, and the president was very concerned about the security of our personnel.

"When we finally were informed that those individuals who were able to go in that compound … found an individual that they believed was bin Laden, there was a tremendous sigh of relief."

'Watershed' moment

United Nations Secretary General Ban Ki-moon called bin Laden's death a "watershed" moment in the fight against terrorism.

U.S. Secretary of State Hillary Clinton said the "battle to stop al-Qaeda and its syndicate of terror" is not over. The U.S. will continue to "take the fight" to the Taliban and others in Afghanistan who are sympathetic to al-Qaeda, she said.

"This guy is gone, he's dead. And what al-Qaeda has lost is their intellectual head," former U.S. secretary of state Colin Powell told CNN.

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U.S. President Barack Obama, speaking at the White House on Monday, the day after announcing the death of Osama bin Lade, says it was 'a good day for America.' ((Charles Dharapak/Associated Press))

"Short term there's more danger, long term there's more safety," former New York city mayor Rudolph Giuliani, who gained prominence for his leadership of the city in the days after the Sept. 11 attacks, told CNN.

Almost 3,000 people, including 24 Canadians, died in the attacks that began with the hijacking of four U.S. airliners and ended with the collapse of the twin towers of the World Trade Center.

Security increased

Western countries, meanwhile, beefed up security at some potential targets and it didn't take long for talk of revenge to surface.

A senior al-Qaeda ideologue posted a long eulogy for bin Laden on extremist websites and promised to "avenge the killing of the Sheik of Islam."

Brennan denied reports that taking bin Laden prisoner was never an option. He said bin Laden would have been taken alive had the opportunity presented itself, but he fought back and was killed.

Late Monday, senior U.S. officials said bin Laden was killed by a precision shot near the end of the firefight.

The White House also confirmed that no allies were consulted about the mission beforehand. Pakistani television pictures showed flames shooting from the roof of bin Laden's house into the night sky.

Officials said his body was put aboard the USS Carl Vinson, where traditional Islamic procedures for handling the remains were followed, including washing the corpse, placing it in a white sheet and committing the body to the waters of the North Arabian Sea.

DNA proof

Pentagon officials said DNA analysis provided "99.9 per cent" certainty that the body was indeed that of bin Laden.

The government said it had a photo of bin Laden's body but hadn't decided whether to release it.

"We are going to do everything we can to make sure that nobody has any basis to try to deny that we got Osama bin Laden,"  Brennan said.

The U.S. will "share what we can because we want to make sure that not only the American people but the world understand exactly what happened."

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In this file picture, Osama bin Laden is seen at an undisclosed location in a television image broadcast. (CBC)

Many family members of victims of the Sept. 11 attacks expressed relief that the long hunt for bin Laden had finally come to end.

Canadian Hans Gerhardt, whose son Ralph died in the collapse of the twin towers, said he had mixed feelings about the news but called the killing of bin Laden "the right thing to do."

"It was a sweet-sour kind of victory, a muted victory, because it brought back all the emotions of, you know, what we lost and the terror of 9/11."

Montreal resident Bob Ewart, who lost his daughter and son-in-law in the attacks, said he didn't feel like cheering.

"Good riddance to a person the world can do without," he said. "It doesn't make the world a safer place with his death."

With filesfrom The Associated Press