Singapore's founding prime minister Lee Kuan Yew paid tribute to Nelson Mandela in a condolence letter to his widow on Friday, calling him "an inspiration to an entire generation".

In the letter, addressed to Madam Gracha Machel, Mr Lee described the former South African president as "a charming and unassuming man".

"Nelson was an inspiration to an entire generation. Without him, South Africa would not be the democratic and multiracial nation that it is today," Mr Lee wrote.

"A charming and unassuming man, he will be remembered and missed by millions. My deepest condolences on his passing."

Mr Lee had met the late Mr Mandela on several occasions, including a 13-day visit in 1992 to South Africa.

Mr Mandela subsequently visited Singapore in March 1997, in the first state visit by a South African head of state to the Republic.

Mr Mandela was 95 and died peacefully at his Johannesburg home on early Friday morning, Singapore time, after a prolonged lung infection.