Juan Guaido, recognized by the United States and some 50 other countries as the interim President of Venezuela, warned the military on Sunday that preventing the entry of humanitarian aid into Venezuela is a "crime against humanity" and makes them "almost genocidal."
"There are people responsible for this and the regime knows it. This is a crime against humanity, men of the armed forces," Juan Guaido said. He directed his comments at soldiers deployed to a bridge connecting Venezuela with Colombia.
Shipments of U.S. food, medicine, and humanitarian aid are on the Colombian side, with a tanker and two large trucks sitting in the middle of the bridge.
WATCH: US sends aid to Venezuela
Venezuelan President Nicolas Maduro has ordered the soldiers to prevent the aid from crossing the border.
Maduro has said the U.S. help is part of a plot to overthrow his government and said Venezuela doesn't need it.
But a Venezuelan doctor who was part of a protest Sunday accused Maduro of sinking Venezuelan medicine to a "medieval" level.
Maduro appeared on state television Sunday, showing off anti-aircraft systems and other weapons he says will make Venezuelan cities "impregnable."
"We are a pacifist people as long as no one messes with us, that Donald Trump does not threaten us," Maduro said. "Donald Trump, get out of Venezuela. Out with his threats. There are armed forces here and a people to defend the honor, dignity, and decorum."
Trump has not ruled out U.S. military action for Venezuela, but has not specified under what circumstances he would send in U.S. forces.
The U.N. Secretary General is expected to meet with Maduro's foreign minister, Jorge Arreaza, Monday night in New York.
The United States was the first to recognize Guaido as the president of Venezuela, followed by Canada, and many Latin and European nations.
Guaido declared himself interim president on January 23. He said Maduro's re-election was fraudulent and as head of the opposition-led National Assembly, he had the constitutional right to invalidate the results and declare himself president until a new election is held.
Maduro is refusing to step down or call for a new election, accusing the U.S. of orchestrating a coup attempt.
A drop in energy prices, corruption, and failed socialist policies have destroyed the oil-rich Venezuelan economy, leaving severe shortages of food and medicine and out-of-control inflation.