Al-Qaeda mastermind Osama bin Laden, in hiding since the attacks of September 11, 2001, has been killed in an attack on a compound outside Islamabad, Pakistan, on May 1, 2011, as confirmed by U.S. President Barack Obama in a historic late Sunday evening statement from the East Room of the White House.  News of bin Laden's death initially broke on Twitter ahead of the official announcement.  Bin Laden's body has been buried at sea.

While citizens of the United States awaited a late Sunday evening statement from President Barack Obama, hastily announced for 10:30 p.m. EDT about an hour earlier, word leaked from several sources, confirmed by the New York Times, that the president would confirm that Osama bin Laden, the Al-Qaeda mastermind of the 9/11 attacks ten years ago, has been killed and the U.S. has possession of the body.

According to CNN's John King, bin Laden was killed by "actionable U.S. intelligence by U.S. assets."   CNN's Ed Henry reports are that he was in a mansion outside the Pakistan capital of Islamabad and was killed with other family members.   CNN is also reporting that the asset used to kill bin Laden was human and not a drone, and that Pakistani government officials confirmed it was a high level intelligence operation which included their cooperation.

Media advises that the military was placed on a higher state of alert in conjunction with the news, which could raise national security concerns. 

News of bin Laden's death spread quickly on Twitter and elsewhere in social media online as the president's statement was delayed.   Chanting and cheering crowds gathering outside the White House spontaneously erupted into the national anthem.

President Obama had not yet made a statement by 11:30 p.m. EDT. 

Update:  President Barack Obama made a statement from the East Room of the White House at 11:35 p.m. EDT, confirming the death of bin Laden as the result of an operation earlier in the day near Islamabad.  According to Obama, a firefight ensued but no Americans were harmed.   The president confirmed that the death of bin Laden was the #1 objective of the war on terror, and that by last week he felt he had enough intelligence to order targeted action.  The identity of the body has been confirmed.

The president's statement concluded at 11:44 p.m. EDT. 

According to further reporting by CNN, the president held five National Security meetings in March and April to plan this operation, and took advantage this weekend of the fact that most of the world was watching the royal wedding to time the apparently successful attack on bin Laden.   

The attack, said to have lasted less than forty minutes, was carried out in Abbottabad, Pakistan, by a helicopter drop of U.S. Navy Seals, who practiced several times before the actual operation took place.   Three men, including one of Osama bin Laden's sons, and a woman who was used as a human shield, were killed in the operation.  A U.S. helicopter that malfunctioned on landing in the operation was later destroyed by U.S. forces.

CNN has confirmed that bin Laden was shot in the head.  Officials reported that the corpse has been handled "according to Islamic practice."  It was later announced that his body was committed to the sea within twenty-four hours of his death.

The historic news was apparently first leaked on Twitter at 10:25 p.m. EDT, just ahead of the president's scheduled televised announcement, by Keith Urbahn, former chief of staff to Donald Rumsfeld.  Former President George W. Bush had been informed of the news earlier in the day.   Urbahn claims his source was a "connected network TV news producer."  "As much as I believe in the rise of 'citizen journalism,' blogs, twitter etc supplanting traditional media," he tweeted early this morning, "my tweet isn't great evidence of it."

On the Web:

Bin Laden Dead, U.S. Official Says - The New York Times 

Al-Qaeda Leader Bin Laden Dead - BBC 

Hunting Bin-Laden - Frontline/PBS 

Live-streaming of President Obama's statement on the death of bin Laden - KABC-TV, Los Angeles 

Obama: Al-Qaida Head Bin Laden Dead - AP (video)

Why Was Bin Laden Buried at Sea So Quickly? - TIME 

How the Bin Laden Announcement Leaked Out - The New York Times (Media Decoder Blog)

Obama's bin Laden Remarks: Full Text - Salon 

Please see also Saturn Smith's excellent live blog tonight on Open Salon: Liveblog, a bit:  Bin Laden Dead, Obama to Speak