Cuba's parliament has opened a session in Havana, and for only the second time in 30 years, longtime ruler Fidel Castro is not in attendance.

His brother, Acting President Raul Castro said earlier this week that the ailing revolutionary leader is "irreplaceable."

But Raul Castro added that the revolutionary generation has a duty to pass the leadership on to a younger generation, whether it wants to or not.

Fidel Castro made his brother acting president in late July while recovering from intestinal surgery. Details of the 80-year-old's health are closely guarded.

The director of U.S. national intelligence, John Negroponte, has said that Mr. Castro is very ill and could die within months, rather than years.

Some information for this report was provided by AFP, AP.