Amnesty International secretary-general Kumi Naidoo has announced he will step down from his post, citing medical reasons. Naidoo will take a period of medical leave from January to honour long-standing commitments in December, should his health permit.He said in a statement on Thursday that while he considers Amnesty International "one of humanity's most important global assets", it needs a leader who is "fighting fit"."Now, more than ever, the organisation needs a secretary-general who is fighting fit and can see through its mandate with vitality that this role, this institution and the mission of universal human rights deserve," Naidoo said. He added: "It has been a huge privilege to have worked with our excellent and committed staff and volunteers at the international secretariat as well as with our sections. "I have been inspired by the important and courageous work being done by our movement. But due to my health, I have no choice but to take this painful decision and step down. I need to recover my health and figure out a more sustainable way to continue to contribute to the struggle for justice in the future.”The organisation confirmed that Naidoo’s resignation has been accepted by the international board, and that he will be handing over his duties on Friday.Naidoo took to Twitter to bid farewell, saying he needed time to recover his health.It has been one of the greatest honours of my life to lead @amnesty. But it is with a heavy heart that I'm announcing today that I've taken the decision to step down in order to prioritize my health and get back to fighting fit. (1/3)— Kumi Naidoo (@kuminaidoo) December 5, 2019 According to the organisation, Naidoo has a pre-existing medical condition which has worsened in recent months.His duties will be handed over to deputy secretary-general Julie Verhaar until a replacement can be found. Sarah Beamish, chair of Amnesty International's international board, said Naidoo contributed to shaping a global strategy to fight human rights abuses. "It is with reluctance, but understanding, that we have accepted Kumi's resignation. During his tenure as secretary general he has shown true leadership, helping us shape our next global strategy and ensuring that we can meet the human rights challenges facing the world."