Al-Qaeda leader Osama Bin Laden has been killed by US forces at his compound in north-west Pakistan.

Crowds have flooded the streets of Washington and New York reacting to news of his death with both jubilation and trepidation, as BBC correspondents report.

Washington

The crowds started gathering outside the White House even before President Obama delivered the news.

Word spread quickly as US television networks gave advance warning of what he was going to say.

Crowds chanted "USA USA" outside the White House

People were running towards Lafayette Square, the park outside the White House, to join the celebrations.

Some climbed into the trees outside, stringing US flags - the Stars and Stripes - between the branches.

Chants of "USA, USA, USA" surged from the growing crowd.

Until now, President Obama and most other US politicians barely mentioned Osama Bin Laden's name, trying to play down his importance, and not wanting to draw attention to the fact he had not been found.

But there was no doubting how Americans see him - as their public enemy number one. His death is hugely symbolic.

There was a mood of euphoria and relief in the square.

People said they wanted to be there for this moment. They remembered where they were on 11 September 2001. They said they would remember this moment in the same way.

It represents "closure", said one woman.

The crowd was mostly young people, many of them students from Washington colleges and universities.

Someone had found an old campaign poster for the last occupants of the White House, holding aloft the words Bush-Cheney - the men who took on the hunt for Bin Laden after 9/11.

Behind the iron fence around the White House, extra secret service agents looked on.

But amid the celebrations there were also plenty of sober voices - worried at what comes next.

Many spoke of fears of al-Qaeda's response. Osama Bin Laden's deputy Ayman al-Zawahiri is still believed to be in hiding.

President Obama reflected that caution in his statement.

But for him this is already being seen as a huge personal triumph.

And in the crowd there were chants of four more years for Obama.

New York

Despite the late hour of the announcement, hundreds gathered in the streets of New York to celebrate the death of the man behind the 9/11 attacks on their city.

There was jubilation, and a strong sense of patriotism.

In Times Square people waved American flags, shouting "USA, USA" as passing vehicles honked their horns.

At one point a diva broke into a full-throated rendition of the national anthem that would not have sounded out of place in an opera house. Elsewhere dozens recited the US pledge of allegiance.

"I'm glad it was us who nailed him," said one man, Rick, reflecting a prevalent sense of retributive justice.

Another man, Eric, rejoiced at some rare good news.

"I'm feeling ecstatic that there's a lot of positive energy here, because there's been a lot of negativity for many years," he said, adding that the news would give US troops a major morale boost.

Amidst the triumphalism there were those who took time for reflection and at Ground Zero some lit candles in memory of the 9/11 victims.

But there was also apprehension - one woman said the death of Osama Bin Laden brought at least symbolic closure to a traumatic period, but many feared an al-Qaeda retaliation.

"I am celebrating tonight but I fear for tomorrow," said another woman.

Many also believed the demise of the 9/11 mastermind would have no impact on the wars in which the US had become embroiled in response to the attacks.