"The UN can be improved, it is not perfect but if it didn't exist you would have to create it," he told the BBC's Hard Talk during an interview for his 80th birthday last April, recorded at the Geneva Graduate Institute where he had studied.

"I am a stubborn optimist, I was born an optimist and willremain an optimist," Annan added.

UN High Commissioner for Human Rights, Zeid Ra'adal-Hussein, paid tribute to Annan as "humanity's best example,the epitome, of human decency and grace".

Zeid, who has criticised major powers and other countries during his four-year term that ends later this month, said that whenever he felt "isolated and alone politically", he would go for long walks with Annan in Geneva.