Al Qaeda leader Osama bin Laden was killed in a U.S. helicopter raid on a mansion near the Pakistani capital Islamabad early on Monday, ending a long worldwide hunt for the mastermind of the Sept. 11, 2001, attacks on the United States.

Members of an elite Navy Seals team dropped by helicopter to the compound were under orders to kill not capture bin Laden, who had eluded U.S. forces for 13 years, a senior U.S. security official told Reuters.

"This was a kill operation," the official said, speaking on condition of anonymity.

Many analysts see bin Laden's death as largely symbolic since he was no longer believed to have been issuing operational orders to the many autonomous al Qaeda affiliates around the world.

Fearful of revenge attacks, the United States swiftly issued security warnings to Americans worldwide. A top Republican lawmaker briefed by the White House on bin Laden's death said U.S. security agencies were working to prevent any attacks on the United States or its installations overseas.

"This is a key moment because al Qaeda has to avenge. This is a terrible defeat for them and they have to move as quickly as they can, and it's up to us to stop them," said congressman Peter King.

Bin Laden's death is unlikely to have any impact on the nearly decade-long war in Afghanistan spawned by the Sept. 11 attacks on Washington and New York. U.S. forces there are facing record violence by a resurgent Taliban, which has vowed to avenge his death.

President Barack Obama, whose popularity has been hit hard by rising gasoline prices, will likely see a short-term bounce in his approval ratings. But he may also come under more pressure from Americans to speed up a planned withdrawal of U.S. forces from the unpopular war in Afghanistan.

U.S. officials said bin Laden was found in a million-dollar compound in the military garrison town of Abbottabad, 35 miles (60 km) north of Islamabad. After 40 minutes of fighting, bin Laden was among several people in the mansion killed.

A source familiar with the operation said bin Laden was shot in the head. A senior U.S. official in Washington said the al Qaeda leader was killed in a firefight after he resisted the assault force.

Two officials, speaking on condition of anonymity, said bin Laden was buried at sea. A third official said this was done to prevent a gravesite on land becoming a shrine for followers.

"Justice has been done," Obama declared in a dramatic late-night White House speech announcing the death of the elusive head of the militant Islamic group behind a series of deadly bombings across the world.

PAKISTAN TOLD AFTER RAID

Leaders worldwide praised the killing as a dramatic success in the war against al Qaeda, a mood reflected in financial markets. The dollar and stocks rose, while oil and gold fell, on the view bin Laden's death reduced global security risks.

Thousands of jubilant, flag-waving Americans thronged outside the White House and in the streets of New York after Obama's announcement.

It was the biggest national security victory for the president since he took office in early 2009 and will make it difficult for Republicans to portray Democrats as weak on security as he seeks re-election in 2012.

In sharp contrast, on the streets of Saudi Arabia, bin Laden's native land which stripped him of his citizenship after Sept. 11, there was a mood of disbelief and sorrow among many.

The Palestinian Islamist group Hamas mourned bin Laden as an "Arab holy warrior."

But many in the Arab world felt his death was long overdue. For many Arabs, inspired by the popular upheavals in Egypt, Libya and elsewhere over the past few months, the news of bin Laden's death had less significance than it once might have.

The operation could complicate relations with Pakistan, a key U.S. ally in the battle against militancy and the war in Afghanistan. Those ties have already been frayed over U.S. drone strikes in the west of the country and the six-week imprisonment of a CIA contractor earlier this year.

A U.S. official said Pakistani authorities were told the details of the raid after it had taken place.

The revelation bin Laden was living in style will hugely embarrass Pakistani officials, who will be under pressure to explain how he could have been right under their noses. Residents in Abbottabad said a Pakistani military training academy is near the compound.

"For some time there will be a lot of tension between Washington and Islamabad because bin Laden seems to have been living here close to Islamabad," said Imtiaz Gul, a Pakistani security analyst.