CÚCUTA, Colombia — President Nicolás Maduro of Venezuela broke relations with Colombia on Saturday, furious over Colombia’s assistance to the Venezuelan opposition in its ambitious effort to truck foreign aid into the country in defiance of his blockade orders.

“Patience is exhausted, I can’t bear it anymore, we can’t keep putting up with Colombian territory being used for attacks against Venezuela,” Maduro said in a speech in Caracas, the capital. “For that reason, I have decided to break all political and diplomatic relations with Colombia’s fascist government.”

He gave Colombian diplomats 24 hours to leave.

The diplomatic break sharply escalated tensions between the Latin American neighbors on a day when hundreds of anti-Maduro protesters along Venezuela’s borders with Colombia and Brazil tried to pierce the blockade, with only scattered success. Much of the day was punctuated by violence as security forces battled protesters.

At least two people were killed in southern Venezuela near the Brazil border, hospital officials said, and clashes between the police and anti-Maduro demonstrators upended peaceful marches in Venezuela near bridge crossings with Colombia.

A pickup truck of aid crossed into Venezuela from the northern Brazilian town of Pacairama, in what opposition figures said was a small but symbolic success.

“We did it,” said María Teresa Belandria, who is the Brazil envoy of the Venezuelan opposition leader, Juan Guaidó. “This is a major victory.”

Still, as of midday, no sign of any major breaches appeared elsewhere in the blockade. And trouble erupted as a march near a footbridge to Colombia degenerated into running battles between young protesters and security forces.

That march, in the Venezuelan border town of Ureña, was meant to clear a path for aid to be delivered via a footbridge blocked by Maduro’s forces. Locals defied the government’s orders and tried to storm the bridge, but Venezuelan security forces fired tear gas to disperse them, and clashes left a trail of damage and burning vehicles.

Protesters in Ureña also stormed a school where 100 government militia members — many of them retirees — were staying. Some joined the protesters.

Guaidó, the 35-year-old leader of the opposition who claims to be Venezuela’s rightful leader, said from the Colombian side of the border that he hoped the Venezuelan security forces would stand aside and allow the aid in.

“Anyone who is not on the side of the people and who prevents the entry of humanitarian aid is a deserter who betrays our people,” Guaidó said in a Twitter post. “Those who accompany us to save the lives of Venezuelans are true patriots.”

Earlier Saturday, Guaidó posted on Twitter that “several members” of the national guard assigned to the Simón Bolívar International Bridge that connects Venezuela and Colombia had joined the opposition. He posted a video showing three men wearing Venezuelan military police uniforms, escorted by a police officer on the Colombian side of the border.

“They have decided to stand on the side of the people and the constitution!” he wrote in a message. “Welcome! The arrival of freedom and democracy to Venezuela is already unstoppable.”

In a foretaste of the confrontation over aid, Venezuelan security forces near the Brazil border opened fire on a crowd blocking access to a road Friday, killing two people and injuring a dozen others.

As evening fell Friday, Maduro’s government added three bridges along the Colombian border to a growing list of port of entry closures that included the borders with Brazil and three Caribbean islands, effectively sealing off most of Venezuela’s main entry points by land and sea.

As the sun rose Saturday morning, several hundred Venezuelans had gathered in an empty lot beside the Tienditas Bridge here in Cúcuta, under a massive flag hung from a crane. Many slept on open ground in the makeshift camp as opposition activists organized prayer circles and danced to salsa music, calling for the downfall of Maduro.

“I know it’s been a long night but we are moving ahead,” an opposition member, Adolfo Marín, said to the crowd. “Remember we have a blockade, but manpower is supernatural, believe me, with a small group of people we can move these containers with a push and a shove.”

“The soldiers of the lower and middle classes today need humanitarian aid, too,” Victor Barboza, an organizer in the camp, said of the security forces waiting on the other side of the bridge. “They have a child who eats just one meal a day. They have a sister who can’t get medication for her illness.”

The border showdown has become one of the most tense and unusual in the region’s history.

Guaidó has been recognized as Venezuela’s interim president by more than 50 countries, including the United States. He has staked his challenge to Maduro on a promise that he will do what the president refuses to: open the country, which suffers from deadly shortages of food and medicine, to international aid shipments.

The White House has waded deep into the standoff, authorizing shipments of aid on military planes and holding a rally at which President Trump warned Venezuela’s military to abandon Maduro or “lose everything.” In response to the killings Friday, the White House issued a statement strongly condemning the use of force by Maduro’s government, warning that rights violations “will not go unpunished,” and urging the military to “uphold its constitutional duty to protect the citizens of Venezuela” and allow aid to enter the country.

Maduro now claims that the aid containers are part of a plot that will lead to an American invasion. His government erected shipping containers on the Tienditas Bridge to keep the aid out.

Some Colombians expressed sympathy with Guaidó’s cause and solidarity with those on the other side of the border.

“We’ve come to help Venezuelans,” said Claudia Pérez, a 38-year-old resident of Cúcuta, which has been hit hard by a wave of Venezuelans fleeing the country. “We on the border have suffered because public services have deteriorated because of overpopulation and growing insecurity.”

On the Venezuelan side of the border, soldiers interviewed said their morale was low. Many said they faced the same shortages of food as the protesters and said they did not want to fire on them if they stormed the bridge.

But the presence of pro-government armed groups known as “colectivos” raised concern about the possibility of violence. They were beginning to appear on the border by early Friday evening, mingling with other government supporters.

Jorge Gil, 50, from the Venezuelan city of Guatire, said he had come to Cúcuta last year after the death of his wife, who had a brain injury and could not find medicine. As he awaited whatever happened next on the bridge, he remembered better times in Venezuela.

“My youth was lovely,” he said. “I enjoyed it and my children so much. It wasn’t that I was rich, but I had good work.”