Osama bin Laden, the mastermind of the worst terrorist attacks on American soil, is dead, officials said -- almost 10 years after the attacks that killed about 3,000 people. The founder and leader of al Qaeda was killed by U.S. forces Monday in a mansion in Abbottabad, north of the Pakistani capital of Islamabad, along with other family members, a senior U.S. official told CNN. In an address to the nation Sunday night, U.S. President Barack Obama called bin Laden's death "the most significant achievement to date in our nation's effort to defeat al Qaeda." "Today, at my direction, the United States launched a targeted operation against that compound in Abbottabad, Pakistan," Obama said. "A small team of Americans carried out the operation with extraordinary courage and capability. 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." A congressional source familiar with the operation said bin Laden was shot in the head. A U.S. official told CNN that bin Laden was buried at sea. The official said his body was handled in the Islamic tradition, but did not elaborate. Half a world away, the scene outside the White House was one of pure jubilation. Hundreds reveled through the night, chanting "USA! USA!" Others chanted "Hey, hey, hey, goodbye!" in reference to the demise of bin Laden. Many also spontaneously sang the national anthem. In New York, a cheering crowd gathered at ground zero -- the site where the twin towers of the World Trade Center once stood. Strains of "God Bless America" could be heard intermittently trickling through the crowd. One former New York firefighter -- forced to retire due to lung ailments suffered as a result of the dust from ground zero -- said he was there to let the 343 firefighters who died in the attacks know "they didn't die in vain." "It's a war that I feel we just won," he said. "I'm down here to let them know that justice has been served." Bob Gibson, a retired New York police officer, said the news of bin Laden's death gave him a sense of "closure." "I never thought this night would come, that we would capture or kill bin Laden," he said. "And thank the Lord he has been eliminated." The news also brought some relief to family members of those killed on 9/11. Jim Riches, who lost his firefighter son when the World Trade Center's north tower collapsed, said he was gratified when he learned of bin Laden's death. "(My) son still isn't coming home," he told CNN. "(There's) no closure, but at last at least some justice for the murder of 3,000 Americans, finally." "This is important news for us, and for the world," Gordon Felt, president of Families of Flight 93, said in a statement. "It cannot ease our pain, or bring back our loved ones. It does bring a measure of comfort that the mastermind of the September 11th tragedy and the face of global terror can no longer spread his evil." Bin Laden eluded capture for years, once reportedly slipping out of a training camp in Afghanistan just hours before a barrage of U.S. cruise missiles destroyed it. He had been implicated in a series of deadly, high-profile attacks that had grown in their intensity and success during the 1990s. They included a deadly firefight with U.S. soldiers in Somalia in October 1993, the bombings of two U.S. embassies in East Africa that killed 224 in August 1998, and an attack on the USS Cole that killed 17 sailors in October 2000. In his speech, Obama reiterated that the United States is not fighting 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," Obama said. The Council on American-Islamic Relations (CAIR), a Muslim civil rights and advocacy organization, released a statement Monday morning welcoming the death of bin Laden. "As we have stated repeatedly since the 9/11 terror attacks, bin Laden never represented Muslims or Islam. In fact, in addition to the killing of thousands of Americans, he and al Qaeda caused the deaths of countless Muslims worldwide," the statement said. While the death of bin Laden "is a significant victory," the war on terrorism is not over, said Frances Fragos Townsend, former Homeland Security advisor to President George W. Bush. "We've been fighting these fractured cells. We've seen the U.S. government, military and intelligence officials deployed around the world," Townsend said. "By no means are these other cells nearly as dangerous as he is, but we will continue to have to fight in chaotic places." U.S. diplomatic facilities around the world were placed on high alert following the announcement of bin Laden's death, a senior U.S. official said, and the U.S. State Department issued a "worldwide caution" for Americans. The travel alert warned of the "enhanced potential for anti-American violence given recent counter-terrorism activity in Pakistan." Some fear al Qaeda supporters may try to retaliate against U.S. citizens or U.S. institutions. More Osama bin Laden is dead.