A group of more than 100 supporters of Cuba's government aggressively heckled dissidents from the communist island attending a civil society forum at a region-wide summit here.

Opponents of President Raul Castro were greeted to shouts of "imperialist" and "mercenaries" as they filed Wednesday into a hotel auditorium to attend speeches by host President Juan Carlos Varela and former U.S. President Bill Clinton.

The heated exchange at a normally sleepy forum for non-governmental organizations across Latin America and the Caribbean highlight the strong emotions hanging over the summit generated by the expected attendance by Cuba's president for the first time and recent sanctions against Venezuelan officials for human rights abuses.