Cuba has held an official day of mourning to mark the death of Defense Minister Julio Casas Reguerio, who passed away Saturday of heart failure at age 75.

In Havana Monday, President Raul Castro took part in a private ceremony to remember Casas, who ran the Cuban military's economic ventures for several years. Several Cuban officials also took part in the ceremony as flags flew at half staff.

Casas was trained as a bank accountant but rose to become one of Cuba's most powerful men. He fought alongside Raul Castro in the 1959 revolution that brought Mr. Castro's brother, Fidel, to power. Raul Castro formally succeeded his brother as president in February 2008.

Observers say the death of Casas has again drawn attention to the issue of Cuba's aging leadership. Raul Castro is 80 years old. Vice President Jose Ramon Machado Ventura is the same age as well.

Fidel Castro, who no longer holds any public office, is 85 years old.