The United States wants to help Cubans prepare for democracy but is not contemplating an invasion of the island in the wake of Fidel Castro's illness, Secretary of State Condoleezza Rice said Sunday.

"The notion that somehow the United States is going to invade Cuba, because there are troubles in Cuba, is simply far-fetched," Rice told NBC. "The United States wants to be a partner and a friend to the Cuban people as they move through this period of difficulty and as they move ahead. But what Cuba should not have is the replacement of one dictator by another."

Still, Cuban authorities have beefed up security by mobilizing citizen defense militias, increasing street patrols, and ordering decommissioned military officers to check in at posts daily.

Cuba's vice president said Castro is recuperating well after surgery for intestinal bleeding. The ailing leader turns 80 on Aug. 13. On Monday it was announced that Castro had temporarily handed over power to his brother Raul, 75.

Rice said, "My message to the Cuban people would be that they have an opportunity, as this unfolds, at home to build a stable and more democratic Cuba."

When asked whether the United States expects large numbers of Cubans to flee the island for America, Rice said that U.S. officials have worked "to tell the Cuban people that their future is at home, and no, a mass exodus is not to be expected, nor would it be condoned."