Geneva - The head of the World Health Organisation says he is "rethinking" his appointment of Zimbabwe President Robert Mugabe as a "goodwill ambassador".In a new tweet, Tedros Ghebreyesus says that "I'm listening. I hear your concerns. Rethinking the approach in light of WHO values. I will issue a statement as soon as possible."The appointment of Mugabe has been met with widespread shock and condemnation, including from the United States, which sanctioned him more than a decade ago over his government's human rights abuses.The 93-year-old Mugabe has been criticised at home for going abroad for medical treatment as his once-prosperous country's economy suffers.