Obama has won praise across much of Latin America for seeking to restore diplomatic relations with Cuba and he shook President Raul Castro's hand in a show of the detente on Friday night, but he took a tougher line on Saturday in a speech at the Summit of the Americas in Panama.

"I believe our governments together have an obligation to uphold the universal freedoms and rights of all our citizens," Obama told other leaders from across the Americas. "The voices of our citizens must be heard."

Responding to other leaders' criticism of past U.S. policy in Latin America, including its support of military coups and dictatorships during the Cold War, Obama said Washington's record was far from perfect but that it has changed and he would continue to push for greater democracy.