U.S. President Barack Obama said Sunday that a U.S. operation has killed Osama bin Laden in Islamabad and that the al-Qaida leader's body is in U.S. custody.

Pakistani sources have also confirmed that bin Laden was killed in a compound in Abbottabad outside the capital of Islamabad.

Several other adults were also killed in the strike, one of whom is believed to be an adult son of bin Laden, said the reports.

In a highly unusual Sunday night speech, Obama hailed the death of the terrorist leader as the "most significant achievement" to date in U.S. efforts to defeat al-Qaida.

Earlier in the day, the United States launched "a targeted operation" against the Abbottabad compound, and later confirmed that the terrorist leader was among those killed in a fire fight, said the president.

He said that shortly after taking office in 2009, he asked Leon Panetta, director of the Central Intelligence Agency, to make killing or capture of bin Laden a top priority in the war against al-Qaida.

He added the United States obtained leads about bin Laden last August, and made a preliminary assessment that he was hiding "deep inside" Pakistan.

"Finally, last week, I determined we had enough intelligence to take action, and authorized an operation to get Osama bin Laden, and bring him to justice," Obama said. "Today, at my direction, the United States launched a targeted operation against that compound."

A small team carried out the raid, during which the team killed bin Laden in a fire fight and took custody of his body, he said, adding that no American was harmed.

The president also said that the joint counterterrorist efforts with Pakistan led to the achievement. "Going forward, it is essential that Pakistan continue to join us in the fight against al-Qaida and its affiliates," he said.

Bin Laden, born in Saudi Arabia in 1957 and widely seen as the kingpin of global terrorism, was held responsible for a string of anti-American attacks, including the world-shocking Sept. 11, 2001 terror attack, which killed more than 3,000 people in the United States.

As the news of bin Laden's death went public, a jubilant crowd of hundreds of people gathered outside the White House cheering, applauding and waving U.S. national flaps.

Joe Lombardi, a soldier during 2002 to 2006, said, "I joined the military after 9/11. It brings a closure to the part of my life. It brings a closure for Americans as well."

"We can go home from Afghanistan. Hopefully, we will get out of Afghanistan," he added.

Ben Porter, a student in Washington, said, "I am very happy about that (bin Laden' s death), of course. Hopefully, it is the start of the end to an era of conflict. It is something we have been waiting for a long time, more than ten years."

Former U.S. President George W. Bush, who waged a "war on terror" after the Sept. 11 attacks, said in a statement after Obama's announcement that the death of bin Laden was a "momentous achievement."

Another former President Bill Clinton said: "I congratulate the president, the national security team and the members of our armed forces on bringing Osama bin Laden to justice after more than a decade of murderous al-Qaida attacks."

Shortly after Obama's speech, amid fears of retaliatory anti-American violence, the U.S. State Department issued a global travel alert to U.S. citizens, and put all the U.S. embassies on alert.