Updated

Fidel Castro (search) accused Mexican Foreign Secretary Luis Ernesto Derbez (search) of being an "agent" of the United States Monday in a stinging critique of the diplomat, who is neck-to-neck with Chile's interior minister in a race to head the Organization of American States (search).

In televised remarks, the Cuban president also called the Mexican diplomat "pretentious" and "failed" in the latest chapter of Mexico-Cuba tensions.

"They (Latin American countries) don't stop being coaxed by this agent," Castro said. "Let's give him a more honorable title: candidate of the (U.S.) empire ... who wants to keep plundering this hemisphere."

Derbez is running up against Chilean Interior Minister Jose Miguel Insulza for the position of secretary-general of the OAS. The organization was unable to elect a winner last week, as the candidates remained tied in five secret voting rounds, and will reconvene May 2.

Cuba is the only country in the hemisphere that is not a member of the OAS, an organization Castro called "rubbish" on Monday.

Cuba's relations with Mexico, once the communist country's strongest ally, have been rocky since President Vicente Fox took office in 2000.

Last May, both countries withdrew their ambassadors after Mexico accused Cuba of meddling in its internal affairs. A visit by Derbez to the island in July helped thaw the diplomatic freeze, however, and ambassadors were reinstated.

But Castro expressed disappointment that Mexico supported a U.S.-backed resolution last week for the U.N. Human Rights Commission (search) criticizing Cuba's rights record, saying Mexico's vote was an act of "betrayal" done in exchange for U.S. support for Derbez's OAS candidacy.