Osama Bin Laden spent his final months in hiding worrying about the future of Al Qaeda, emails recovered from computers in his hideout reveal.

The terror leader was spending as much of his time dealing with concerns about funding and the toil being taken by CIA drone explosions as he was plotting attacks, according to U.S. intelligence officers.

Officials said the emails depict an organisation beset by mounting problems as its leader remained obsessed on a follow up attack to September 11.