Osama bin Laden, the world's most wanted man, is dead, US president Barack Obama confirmed.

Osama bin Laden, the world's most wanted man, is dead, US president Barack Obama confirmed today.

The man held responsible for the terrorist attacks in New York on September 11, 2001, and the London bombings of July 7 2005, was killed in a US operation in Pakistan.

Speaking from the White House, president Obama said he authorised the operation. The body of the al-Qaeda leader was now in US custody, he said.

Mr Obama said it was 'the most significant achievement to date in our nation's effort to defeat al-Qaeda'.

The US has put its embassies around the world on alert, warning Americans of the possibility of al-Qaeda reprisal attacks for Bin Laden's killing.

Crowds gathered outside the White House in Washington DC, chanting 'USA, USA' after the news emerged.

Bin Laden had evaded the forces of the US and its allies for almost a decade, despite a $25m bounty on his head.

Mr Obama said he had been briefed last August on a possible lead to Bin Laden's whereabouts.

'It was far from certain, and it took many months to run this thread to ground,' Mr Obama said.

'I met repeatedly with my national security team as we developed more information about the possibility that we had located Bin Laden hiding within a compound deep inside of Pakistan.

'And finally, last week, I determined that we had enough intelligence to take action, and authorised an operation to get Osama Bin Laden and bring him to justice,' the president said.

On Sunday a team of US forces undertook the operation in Abbottabad, 100km (62 miles) north-east of Islamabad.

After a 'firefight' Bin Laden was killed and his body taken by US forces, the president said.

Mr Obama said 'no Americans were harmed'.

UK prime minister David Cameron today hailed Bin Laden's death as a 'great success'.

'The news Osama bin Laden is dead will bring great relief to people across the world,' Mr Cameron said, adding later it would be welcomed across the UK.

'Osama Bin Laden was responsible for the worst terrorist atrocities the world has seen - for 9/11 and for so many attacks, which have cost thousands of lives, many of them British.

'It is a great success that he has been found and will no longer be able to pursue his campaign of global terror.'

Giving more details of the operation, a senior US official said a small US team had conducted the raid in about 40 minutes.

One helicopter was lost due to 'technical failure'. The team destroyed it and left in its other aircraft.

Three other men were killed in the raid - one of Bin Laden's sons and two couriers - the official said, adding that one woman was also killed when she was used as 'a shield' and two other women were injured.

The size and complexity of the structure in Abbottabad had 'shocked' US officials.

The US official said that intelligence had been tracking a 'trusted courier' of Bin Laden for many years. The courier's identity was discovered four years ago, his area of operation two years ago and then, last August, his residence in Abbottabad was found, triggering the start of the mission.

Another senior US official said that no intelligence had been shared with any country, including Pakistan, ahead of the raid.

'Only a very small group of people inside our own government knew of this operation in advance,' the official said.

The Abbottabad residence is just 700m (800 yards) from the Pakistan Military Academy - the country's equivalent of West Point.

The senior US official warned that the possibility of revenge attacks had now created 'a heightened threat to the homeland and to US citizens and facilities abroad'.

But the official added that 'the loss of Bin Laden puts the group on a path of decline that will be difficult to reverse'.