Ecuadorean President Rafael Correa will boycott this month's Summit of the Americas in Colombia because Cuba is not invited, he told the host in a letter Monday.
The announcement by the leftist president makes him the first of 34 invited presidents to decline to attend the April 14-15 summit of the continent's leaders in Cartagena, Colombia.
U.S. President Barack Obama is among hemispheric leaders slated to attend the summit.
Correa had proposed last month that presidents of the leftist Bolivarian Alliance, which also includes Venezuela, Bolivia and Nicaragua, boycott the summit. But the presidents of all three nations have confirmed their attendance.
In his letter to President Juan Manuel Santos of Colombia, Correa called the U.S. veto of Cuban participation "intolerable" and said its exclusion was not the result of consensus.
"It is unacceptable in these summits fundamental topics are avoided such as the inhuman blockade of Cuba and the aberrant colonization of the Malvinas Islands," he wrote, backing Argentina's claim to the disputed Falkland Islands.
The letter was read by presidential spokesman Patricio Barriga and posted on the presidential website. In it, Correa called his absence an "invitation to debate the essential and act with consequence."
Washington opposes Cuban inclusion in the regional summit, which is held every three years.
The summit is historically linked to the Organization of American States, which many of the region's governments complain is unfairly dominated by Washington.
Cuba has not participated in the OAS since 1962 but has expressed a desire to attend the Cartagena summit.
U.S. officials say Cuba, ruled since 1959 by brothers Fidel and Raul Castro, does not meet OAS standards of democracy and thus has no business taking part.