Ban Ki-moon, the outgoing UN secretary-general, says he laments not ending conflicts or doing more to promote peace as he ends 10 years at the UN.
Thronged by UN staff as he made his way out of UN headquarters on Friday, the South Korean diplomat thanked his colleagues, saying it was an honour to have worked with them.
"You should be very proud, just as I am so very proud to call you my colleagues," he said.
The 72-year-old transfers stewardship of the world body to Antonio Guterres, a former Portuguese prime minister, amid continuing conflicts in Syria, Yemen, Mali, the Central African Republic and Libya, to name but a few.
Ban said he lamented the "fires still burning", and in a rare show of criticism of world leaders, criticised unnamed presidents, prime ministers and monarchs for the turmoil.
Singling out Syria, he said he could not understand why it was being held hostage to "the destiny" of Bashar al-Assad.
The Syrian conflict has killed an estimated 400,000 people, contributed to Europe's worst refugee crisis since World War II and allowed the Islamic State of Iraq and the Levant (ISIL) group to emerge as a global threat.
Turning elsewhere, Ban said in his decade at the UN he had endeavoured "to never give up. To keep dreaming, to keep believing, and to keep working hard until we achieve progress".
He urged UN staff to remain focused on advancing UN development goals and work towards addressing issues ranging from climate change to gender empowerment.
Despite serving two terms and being unanimously re-elected in 2011, Ban leaves behind a mixed legacy.
In his first term, he was criticised for not speaking out against human rights abuses in China and Russia.
And, in his second term, for the UN's handling of the cholera epidemic in Haiti and its failure to deal effectively with sexual abuses by UN peacekeepers in the Central African Republic and elsewhere.
His decision to remove an Arab coalition bombing Yemen from a UN blacklist after Saudi Arabia threatened to stop funding UN programmes was sharply rebuked.
On the other hand, he has won plaudits for helping move climate change to the top of the global agenda and strongly backing gay rights despite opposition from many countries.
From Sunday, Guterres, 67, takes over from Ban. He is the first former head of government to lead the UN and will preside over a five-year term.
Source: Al Jazeera News