Castro, 80, was too ill to preside over the Nonaligned Movement's summit, leaving it to acting president Raul Castro, his 75-year-old brother and defense minister, to accept Cuba's three-year chairmanship of the group representing two thirds of the world's countries.
But pictures of Annan visiting the ailing Cuban leader were displayed prominently in Cuban state media Friday, and the U.N. leader thanked him for "his enormous contributions and leadership role."
"The collective mission of this movement is more relevant than ever," Annan said, noting that the world was divided by U.S. and Soviet superpowers when Fidel Castro last hosted the movement in 1979.
Trade among developing nations has grown twice as fast as world trade, he said, creating new opportunities and responsibilities: Developing nations must build now give equal attention to "the three fundamental pillars of development, security and human rights."
"A larger voice brings with it greater responsibility, both internationally and at home," Annan said.
He urged the assembled leaders to fight extreme policy, unemployment and AIDS at home, while also working for peace in the Middle East and a solution to the Israeli-Palestinian conflict.
"The daily violence we are witnessing in Iraq and Afghanistan provides a powerful reminder that, without judicious intervention on the political front, the slide to anarchy and civil war becomes inexorable," he said. "The war in Lebanon has been a wake-up call for many governments around the world."