Updated: 2:19 a.m.

President Barack Obama announced late Sunday that U.S. forces killed Osama bin Laden earlier in the day in Pakistan, nearly 10 years after the Sept. 11 attacks.

Bin Laden’s death “marks the most significant achievement to date in our nation’s effort to defeat the efforts of al-Qaida,” Obama said. Bin Laden was the founder and leader of the terrorist organization of Islamic extremists, which was behind the 2001 attacks on the United States that killed nearly 3,000 people, and he was one of the FBI’s Ten Most Wanted Fugitives.

A small team of Americans carried out the targeted operation Sunday against a compound in Pakistan, where U.S. intelligence officials believed bin Laden was hiding, Obama said from the White House. The U.S. forces killed bin Laden in a firefight and retrieved his body, the president added. Several others on the site were also killed but no Americans were harmed, senior administration officials told reporters during a conference call after the speech.

Obama was first briefed about a lead on bin Laden’s location in August. He repeatedly met with his national security team as it explored the intelligence, and at 8:20 a.m. Friday, before leaving for a tour of tornado damage in Alabama, he gave the final order to carry out the raid.

Obama struck historic tones in his brief remarks, saying that “the images of 9/11 are seared into American history” and that there were “nearly 3,000 citizens taken from us, leaving a gaping hole in our hearts.” He lauded the Americans who joined the military after the terrorist attacks, and he maintained that “we will be relentless in our defense” going forward.

Nineteen al-Qaida terrorists hijacked and crashed four commercial airliners on Sept. 11, 2001: Two struck and collapsed the World Trade Center towers in New York; one struck the Pentagon; and the fourth went down in a field near Shanksville, Pa., after passengers and crew members intervened to keep the hijackers from reaching Washington, D.C. The National Commission on Terrorist Attacks Upon the United States reported in July 2004 that the Capitol or White House may have been the intended target.

The president added that the United States “is not and will not be at war with Islam,” touching on similar comments he has made in the past in an attempt to mend relations with the Muslim world. He also recalled the feelings of unity brought forth following the Sept. 11 attacks and suggested that Sunday’s late announcement should again bring the country together.

“Tonight we are once again reminded that America can do whatever we set our mind to,” Obama said. “That’s the story of our history.”

Obama said he had spoken with Pakistani President Asif Ali Zardari before making his televised announcement, and the two leaders “agree this is a good and historic day for both of our nations.”

After Obama’s speech, senior administration officials explained the operation to reporters, describing the 40-minute firefight as a “surgical raid by a small team.” The officials stressed the “seamless collaboration across government” and said the intelligence community had enough evidence to pursue the compound by mid-February.

An administration official said there have been “countless briefings” and “at least nine” meetings between the president and his top national security team about bin Laden.

“The president was actively involved in reviewing all facets of the operation,” the official added.

The officials also described the compound where bin Laden was killed in extensive detail. Based on what they called “extraordinary” security measures at the compound, intelligence officials believed bin Laden was the likeliest person to be hiding there.

The large home, built five years ago at the end of a dirt road in “an affluent suburb of Islamabad,” was eight times larger than surrounding homes and had 12- to 18-foot walls topped with barbed wire. There were internal walls sectioning off the insides of the compound, two security gates and a terrace with a 7-foot privacy wall. Unlike their neighbors, the residents burned their trash. The home was valued at $1 million but had no telephone or Internet service, and the residents had “no explainable source of wealth.”

“We were shocked by what we saw,” one official said. They concluded it was “custom-built to hide someone of significance.”

The White House said that Obama’s team gathered in the Situation Room at 1 p.m. Sunday and worked all day on the operation. Obama first learned that bin Laden had been “tentatively identified” at 3:50 p.m. By 7 p.m., Obama learned there was a “high probability” bin Laden had been hit.

The officials said there is some concern that the terrorist group could now accelerate its efforts, and they pledged that the United States would stay abreast of any threats.

“We’ve always understood this fight would be a marathon and not a sprint,” one official said, adding that bin Laden is the single largest figure in the fight against terrorism. The official predicted bin Laden’s death would bring about the “eventual destruction” of al-Qaida.

As a crowd of hundreds swelled outside the White House on Sunday night, the cheers and singing could be heard from blocks away.

Obama spent most of Sunday evening writing his brief speech and calling former Presidents George W. Bush and Bill Clinton.

Bush congratulated Obama in a statement, saying, “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,” Bush added.

Clinton called it “a profoundly important moment.”

Before Obama made his announcement, Vice President Joseph Biden spoke with House Majority Leader Eric Cantor (R-Va.), Senate Minority Leader Mitch McConnell (R-Ky.), House Minority Leader Nancy Pelosi (D-Calif.), Senate Armed Services ranking member John McCain (R-Ariz.), Sen. Lindsey Graham (R-S.C.), Senate Minority Whip Jon Kyl (R-Ariz.) and Senate Majority Whip Dick Durbin (D-Ill.), according to a White House official.

Biden watched Obama’s late-night speech from the East Room of the White House. Also there were Secretary of State Hillary Clinton; Leon Panetta, the director of the CIA and the president’s choice to be the next Defense secretary; and Adm. Mike Mullen, chairman of the Joint Chiefs of Staff.

Bill Clark contributed to this report.