CÚCUTA, Colombia — Border standoffs may not get much stranger than this one.

Three presidents, a military plane and a lineup of pop artists brought by a British billionaire arrived at a border city known to few before it became famous as the site of a military blockade by Venezuela’s defiant president, Nicolás Maduro.

Mr. Maduro was determined to keep foreign aid out of his country, and the Venezuelan opposition saw an opportunity. Their plan: to break the blockade on Saturday, a culminating act of defiance meant to force the military to choose between allowing food into a hungry nation and loyalty to Mr. Maduro.

It did not go well. By the end of the day, the military had largely sided with the regime, and a protest planned as peaceful had descended into violent skirmishes. Some of the desperately needed aid was burned at the border, and four people were reported dead.

It was Mr. Maduro who had made the first move.

Earlier this month, as food donated largely by the United States made its way to the Colombian border town of Cúcuta, his government barricaded an already-closed border bridge between Colombia and Venezuela, using tanker trucks and containers.