World leaders warned of revenge attacks after Osama bin Laden was killed in a U.S. assault in Pakistan on Monday that brought to a dramatic end the long manhunt for the al Qaeda leader who had become the most powerful symbol of Islamist militancy.

Click here for full Haaretz coverage on the killing of Osama bin Laden.

President Barack Obama declared the world was a safer and "better place" with bin Laden dead. But the euphoria that drew flag-waving crowds to "Ground Zero" of the Sept. 11, 2001, attack in New York was tempered by calls for vigilance against retaliation by his followers.

The U.S. administration told Israel's ambassador to Washington, Michael Oren, about the killing before Obama made his statement to the press. But not all Americans felt at ease with the spontaneous street celebrations after the Al-Qaida leader's death. "These images of celebrations must look pretty ugly to the world," said one C-Span viewer. "It could bring about another attack."

In Israel, the Israel Airports Authority increased the alert level at the country's airports and border crossings, and security has been heightened around the offices of Israeli airlines abroad such as El Al, Arkia and Israir. The Airports Authority told Haaretz the measures addressed current security needs.

In addition, security has been increased at Jewish institutions across the United States, and the police are more closely monitoring American mosques.

The death of bin Laden, who achieved near-mythic status for his ability to elude capture for more than a decade, closes a bitter chapter in the global fight against al Qaeda, but it does not eliminate the threat of further strikes.

Under bin Laden's leadership, al Qaeda militants struck targets from Indonesia to the European capitals of Madrid and London.

But it was the Sept. 11, 2001, attacks, in which al Qaeda militants used hijacked planes to strike at economic and military symbols of American might and killed nearly 3,000 people, that helped bin Laden achieve global infamy.

Those attacks spawned two wars, in Afghanistan and Iraq, inflicted damage on U.S. ties with the Muslim world that have yet to be repaired, and redefined security for air travelers.

"Even as we mark this milestone, we should not forget that the battle to stop al Qaida and its syndicate of terror will not end with the death of bin Laden," U.S. Secretary of State Hillary Clinton said just hours after bin Laden was killed.

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.

"There are a lot of al Qaeda look-alike cells," said Steve Clemons, a Middle East analyst at the New America Foundation. "Bin Laden was an animating force but there are other ways these groups get oxygen and can remain a threat."

Analysts warned that objections from some Muslim clerics to bin Laden's sea burial could stoke anti-American sentiment. The clerics questioned whether the United States followed proper Islamic tradition, saying Muslims should not be buried at sea unless they died during a voyage.

The United States issued security warnings to Americans worldwide. CIA Director Leon Panetta said al Qaida would "almost certainly" try to avenge bin Laden's death.
France's President Nicolas Sarkozy hailed the killing as a coup in the fight against terrorism, but he, too, warned it did not spell al Qaeda's demise. British Prime Minister David Cameron said the West should be "particularly vigilant."

Vows to avenge bin Laden's death appeared quickly in Islamist militant forums, a key means by which al Qaida leaders have passed on information. "God's revenge on you, you Roman dog, God's revenge on you crusaders," one forum member wrote.

A U.S. national security official said there was no fresh intelligence suggesting new plots against U.S. or other Western interests since bin Laden's death.

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 Saudi Arabia, bin Laden's native land, 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.