However, two witnesses have said they saw the Egyptian doctor al-Zawahiri, Bin Laden's deputy, in a terrorist camp this spring in the north-western Pakistan district of Swat.

In June, a recorded message was ascribed to bin Laden. In it, the founder of Al Qaeda in his usual manner threatened the US and the administration of President Barack Obama.

'The American people should prepare to continue to reap what the leaders of the White House are sowing in the years and decades to come,' he said.

Experts, however, said they doubted that bin Laden himself still organises attacks. But there is no doubt that the 52-year old is a symbolic figure for Islamist terrorism.

Bin Laden's campaign against the US does not only impress extremists. In a survey in Pakistan carried out last summer by the US organisation Terror Free Tomorrow, more than one-third of respondents said they had a positive opinion of bin Laden. Former US president George W. Bush was far behind him at less than 10 percent.

It was Bush who said shortly after the attacks on New York and Washington that bin Laden was deceiving himself if he thought he could escape from the US and its allies.

In spring 2004, a spokesman for the US military in Afghanistan said it was sure it would catch bin Laden that year, but the US government said later that the promise was made in the heat of the moment.

Washington afterward answered questions about bin Laden with the vague statement that he would get the punishment he deserved - it was just a question of when.

However, it was also possible that bin Laden could triumph in the end.

The 2007 Pulitzer Prize-winning book 'The Looming Tower' by US journalist Lawrence Wright, said the 2001 Al Qaeda attacks aimed to provoke the US into invading Afghanistan. It was bin Laden's hope, it said, that the US military would be defeated there just as those of the British and the Soviet Union were.

In view of the ever-worsening security situation in Afghanistan, even the US government would not predict victory there any more.

Its White Paper on US Policy Toward Afghanistan and Pakistan, released in March, said, 'The danger of failure is real and the implications are grave'.