WASHINGTON — Osama bin Laden, the glowering mastermind behind the Sept. 11, 2001, terror attacks that murdered thousands of Americans, was killed in an operation led by the United States, President Barack Obama said Sunday.

“Justice has been done,” said the president in a dramatic late-night announcement at the White House.

A small team of U.S. Navy Seals killed bin Laden in a firefight Sunday at a compound in Pakistan, the president said, and took custody of his remains. American officials said they were being handled in accordance with Islamic tradition.

A jubilant crowd gathered outside the White House as word spread of bin Laden’s death after a global manhunt that lasted nearly a decade.

Former President George W. Bush, who was in office on the day of the attacks, issued a written statement hailing bin Laden’s death as a momentous achievement.

“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.

A Pakistani intelligence official in Islamabad said four helicopters launched the attack in the Bilal area of Abbottabad, about 62 miles north of the capital. One of the helicopters crashed after it apparently was hit by fire from the ground, the official said. He gave no word on casualties.

He said the helicopters took off from a Pakistani air base in the north of the country.

Three adult males were also killed in Sunday’s raid, including one of bin Laden’s sons, whom officials did not name. One of bin Laden’s sons, Hamza, is a senior member of al-Qaida.

Women and children were taken into custody during the raid, he said. He spoke on condition of anonymity because of the sensitivity of the information.

Obama said he ordered the operation after receiving undisclosed intelligence information. Senior administration officials said the terrorist mastermind was found inside a custom-built compound.

They said it appeared to have been constructed to harbor one high-value target and that for undisclosed reasons, officials became clear the hideout was bin Laden’s.

A senior administration official says Obama gave the final order for U.S. officials to go after bin Laden on Friday. The official added that a small team found their quarry hiding in a large home in an affluent suburb of Islamabad. The raid occurred in the early morning hours Sunday.

Administration officials offered some details of the operation.

Based on statements given by U.S. detainees, intelligence officials have known for years that bin Laden trusted one al-Qaida courier in particular and they believed he might be living with him in hiding. In November, intelligence officials found out where he was living, a huge fortified compound surrounded by walls as high as 18 feet high, topped with barbed wire. There were two security gates and no phone or Internet running into the house.

Intelligence officials believed the $1 million home was custom-built to harbor a major terrorist. CIA experts analyzed whether it could be anyone else, but time and again, they decided it was almost certainly bin Laden.

Obama spoke with Bush and former President Bill Clinton Sunday night to inform them of the developments.

Obama struck a less than boastful tone in his brief announcement, although he said the death of bin Laden was “the most significant achievement to date in our nation’s effort to defeat al-Qaida.

“His death does not mark the end of our effort. There’s no doubt that al-Qaida will continue to pursue attacks against us. We must and we will remain vigilant,” he added.

Moments after he spoke, American officials cautioned that the events could lead to heightened threats against the United States.

“The reported death of Osama bin Laden is welcome news, but it in no way eliminates the threat from the terrorism he espoused,” said Sen. Richard G. Lugar, R-Ind., who is the ranking Republican on the Senate Foreign Relations Committee. “This is another reminder that Americans cannot hide from global affairs.

“Americans must continue to be vigilant to ensure that terrorist groups and rogue states do not obtain weapons of mass destruction, a goal that I and many other Americans have sought for 20 years.”

Officials said the U.S. would ensure that bin Laden’s body was handled in accordance with Islamic tradition.

The news that bin Laden was killed close to Islamabad will raise questions of how he managed to evade capture and how long he had been there. Most U.S. intelligence assessments had placed him along the lawless border between Pakistan and Afghanistan.

Officials also said they believe the death puts al-Qaida on a path of decline that will be difficult to reverse, but there was no word on the whereabouts of bin Laden’s second-in-command, Ayman al-Zawahri.

The stunning end to the world’s most widely-watched manhunt came just months before the 10th anniversary of the Sept. 11 attacks on the World Trade Centers and Pentagon, orchestrated by bin Laden’s al-Qaida organization, that killed more than 3,000 people.

The attacks a decade ago seemed to come out of nowhere, even though al-Qaida had previously damaged American targets overseas.

The terrorists hijacked planes, flew one of them into one of Manhattan’s Twin Towers — and, moments later, into the other one.

Both buildings collapsed, trapping thousands inside and claiming the lives of firefighters and others who had rushed to help them.

A third plane slammed into the Pentagon, defacing the symbol of America’s military night. A fourth crashed in rural Pennsylvania after passengers overpowered the hijackers and forced the craft from the air — before it could hit its intended target in Washington.

The attacks set off a chain of events that led the United States into wars in Afghanistan, and then Iraq, and America’s entire intelligence apparatus was overhauled to counter the threat of more terror attacks at home.