Ailing leader Fidel Castro said in a letter read on state television Monday that he does not intend to cling to power forever or stand in the way of a younger generation, but invoked the example of a renowned Brazilian architect who is still working at 100.

"My elemental duty is not to cling to positions, or even less to obstruct the path of younger people, but to share experiences and ideas whose modest worth comes from the exceptional era in which I lived," Castro wrote in the final paragraph of a lengthy letter discussing the Bali summit on global warming.

The 81-year-old Castro has not said when — or even if — he will permanently step aside after temporarily ceding his powers to his younger brother Raul 16 months ago. He has not been seen in public since he made that announcement in July 2006 after undergoing emergency intestinal surgery.

But officially Castro remains the president of Cuba's Council of State, making him the country's head of government and state. Several times a week he pens essays, many of them on international issues that are carried on state media.

"I think like (Oscar) Niemeyer that you have to be of consequence up to the end," Castro wrote in Monday's essay, referring to the Brazilian architect who was honored around the world as he turned 100 on Saturday.

Niemeyer helped design the U.N. headquarters and the main buildings of Brazil's capital, winning in 1988 the Pritzker Architecture Prize — dubbed the Nobel of architecture.

In an essay over the weekend, Castro paid homage to Niemeyer, a lifelong communist who was exiled for several years during Brazil's 1964-85 military dictatorship.