Pervasive criticism of Ban Ki-moon's performance as United Nations secretary-general, from within the organisation and among envoys assigned to it, is raising doubts about his prospects of a second term, according to senior officials and diplomats.

In an untypically robust defence of his stewardship, Mr Ban acknowledged last week that there had been negative assessments. However, he also drew attention to the challenges he had faced since he took the post as a compromise candidate at the start of 2007.