Science fiction writer Arthur C. Clarke listed three wishes on his 90th birthday: for the world to embrace cleaner energy resources, for a lasting peace in his adopted home, Sri Lanka, and for evidence of extraterrestrial beings.

"I have always believed that we are not alone in this universe," he said in a speech to a small gathering of scientists, astronauts and government officials Sunday in Colombo where he lives.

Humans are waiting until extraterrestrial beings "call us or give us a sign," he said. "We have no way of guessing when this might happen. I hope sooner rather than later."

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The British-born author, who moved to Sri Lanka in 1954, has written more than 100 sci-fi books, including "2001: A Space Odyssey."

Clarke, who suffers from post-polio syndrome and is confined to a wheelchair, cut a cake as Sri Lanka's president, visiting astronauts and scientists sang "Happy Birthday."

"Sometimes I am asked how I would like to be remembered," Clarke said. "I have had a diverse career as a writer, underwater explorer and space promoter. Of all these I would like to be remembered as a writer."