Socialist Maduro, 61, will seek reelection Sunday to a third six-year term amid accusations of opposition harassment by an increasingly authoritarian regime.

His government agreed with the opposition last year to hold free and fair elections in 2024, with international observers present — winning a temporary easing of sanctions from the United States.

But he since reneged on some of the conditions, and loyalist institutions barred opposition leader Maria Corina Machado from running against him.

On Friday, Panama said its former president Mireya Moscoso, as well as former leaders Miguel Angel Rodriguez of Costa Rica, Jorge Quiroga of Bolivia and Vicente Fox of Mexico, had their plane held up.

The group, which also included former Colombian vice president Marta Lucia Ramirez, got off to allow the plane, with many Venezuelan voters on board, to take off.