Annan, a Ghanaian national, died in hospital in Bern, Switzerland, in the early hours of Saturday, two of his close associates said.

In Geneva, the Kofi Annan Foundation announced his peaceful death with "immense sadness" after a short illness, saying he was surrounded in his last days by his second wife Nane and children Ama, Kojo and Nina.

Annan served two terms as UN Secretary-General in New York from 1997-2006 and retired in Geneva and later lived in a Swiss village in the nearby countryside.

"In many ways, Kofi Annan was the United Nations. He rose through the ranks to lead the organisation into the new millennium with matchless dignity and determination," UN Secretary-General Antonio Guterres, whom Annan had chosen to head the UN refugee agency, said in a statement.

As head of UN peacekeeping operations, Annan was criticised for the world body's failure to halt the genocide in Rwanda in the 1990s.

"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 will remain an optimist," Annan added.

Australian Associated Press