Political tensions in Venezuela boiled over Saturday as violence broke out at various points along the border, amid the opposition party’s attempts to bring 280 tons of humanitarian aid into the country in crisis. On Venezuela’s border with Brazil, four people were killed and 24 injured after pro-government militias opened fire, according to the nonprofit Foro Penal.

The delivery of $60 million worth of aid — donated by the United States and other countries — into Venezuela has become a central point in the standoff between President Nicolás Maduro and self-declared interim president Juan Guaidó.

Maduro has denied there is a humanitarian crisis in Venezuela and placed national guard troops at the country’s borders to keep the donated food, medical supplies and other emergency assistance out. The Venezuelan people are not “beggars,” Maduro said earlier this month.

Demonstrators throw stones after a truck with humanitarian aid was set on fire at a bridge linking Cucuta, Colombia, and Ureña, Venezuela, on Saturday. (Raul Arboleda/AFP/Getty Images)

Despite this, Guaidó said Saturday that a first shipment of humanitarian aid had already entered Venezuela from its southern border with Brazil, and he promised that additional aid waiting in Colombia would also be delivered to Venezuela, even if it meant forcibly breaking blockades ordered by Maduro.

Some of those aid trucks later crossed the border, only to be set on fire, according to a lawmaker who posted footage of burning vehicles from the scene.

Maduro has responded by rallying his supporters and, Saturday afternoon, announcing he was breaking off diplomatic relations with Colombia, whose leaders have supported Guaidó.

Venezuelans cheer as they surround the first truck with humanitarian aid from the Brazilian government that has arrived in Pacaraima, Brazil, on the border with Venezuela. (Ivan Valencia/AP)

Anti-Maduro protesters try to talk with members of the Bolivarian National Guard of Venezuela who block a crossing at the Brazilian border Saturday. (Joédson Alves/EPA-EFE/Shutterstock)

A separate convoy of 14 trucks full of aid had been held up in Cucuta, a city in Colombia just across Venezuela’s western border, where supplies were being stockpiled for weeks. On Saturday afternoon, Guaidó stated that aid trucks had made their way onto Venezuelan soil but that Maduro’s forces were impeding them from going farther.

“Attention Venezuela! We announce that the trucks with humanitarian aid from Colombia are already in Venezuelan land,” he tweeted. “The usurping regime is blocking its path. They will not be able to stop our irreversible decision to live in freedom.”

Shortly after the trucks reportedly crossed into Venezuelan territory, Gaby Arellano — a congresswoman who opposes Maduro — posted a video saying one of the trucks had been set on fire by the national police.

In the background, a raucous crowd could be seen tearing into what appeared to be boxes marked as aid, as dark clouds of smoke billowed into the sky.

Other people could be seen jumping onto the burning trucks, pushing pallets to the ground and passing boxes around in the smoke-filled air.

Earlier Saturday morning, Guaidó had appeared on the Colombian side of the Tienditas International Bridge, which connects Venezuela and Colombia, and reassured the crowds that humanitarian aid was “on its way.” He appeared with the presidents of Paraguay, Colombia and Chile, as well as the secretary general of the Organization of American States.

Guaidó declared on Twitter that “the day has arrived” in which they would bring humanitarian aid into Venezuela, urging opposition supporters to take to the streets.

“From our borders, by land and sea, we will bring hope, food and medicines for the ones who need it the most,” Guaidó tweeted. “We call everyone to go out massively to the streets in the whole country, to protest in peace at barracks, to urge the armed forces to let humanitarian aid in.”

Like leaders in most Western countries, President Trump has recognized the 35-year-old Guaidó as the legitimate interim president of Venezuela. As protests and border clashes were underway there Saturday, Trump tweeted “God Bless the people of Venezuela!”

Maduro supporters take part in a march Saturday in Caracas. (Yuri Cortez/AFP/Getty Images)

Maduro, however, has accused Trump and the United States of using humanitarian aid to try to stage a “coup.” In Caracas, the capital, on Saturday, thousands of people displayed loyalty to Maduro by marching.

In a forceful speech, Maduro asked the Venezuelan people to reject the threats of “invasion” from Trump and the United States.

“Yankees, go home!” he thundered. “I am a man of the people. I will never be a puppet of imperialism.”

He also chided Guaidó at the rally.

“I formally challenge you to call for elections, you clown,” Maduro said, “to see who has the votes and who wins elections — you clown, you beggar, you puppet of imperialism.”

Venezuelans gather at the Tienditas International Bridge in Cucuta, Colombia. (Mauricio Duenas Castaneda/EPA-EFE/REX/Shutterstock)

At other border points around the country, the situation intensified throughout the day Saturday.

Venezuelan national police stand guard at the Simón Bolívar International Bridge, as seen from Cucuta, Colombia. (Luis Robayo/AFP/Getty Images)

At the Simón Bolívar International Bridge, on Venezuela’s western border with Colombia, four members of the Venezuela National Guard abandoned their posts early Saturday morning. One Venezuelan soldier was overcome with emotion, bursting into tears as he crossed into Colombia to join the opposition party.

“They have decided to stand on the side of the people and the Constitution!” Guaidó tweeted. “Welcome! The advent of freedom and democracy to Venezuela is already unstoppable.”

In subsequent tweets, Guaidó promised amnesty to those Venezuelan soldiers who crossed the border to help the opposition party. They would not be labeled traitors, he said, but instead were “true patriots.”

In Ureña, Venezuela, a border town farther north, clashes became violent as the National Guard fired tear gas into crowds of residents who had been trying to clear a blockaded border bridge. Gunshots could be heard as a convoy of trucks carrying aid tried to cross into Venezuela.

Demonstrators clash with Venezuela's security forces in Urena. (Andres Martinez Casares/Reuters)

A group of opposition supporters stormed a school and chased out pro-government supporters who were holed up there overnight. The opposition shouted “traitors!” at the fleeing loyalists. Images from Ureña included several of a bus that had been set afire in the turmoil.

Opposition demonstrators gesture toward security forces in Ureña. (Andres Martinez Casares/Reuters)

A bus that was torched during clashes with the National Guard burns in Urena, near the border with Colombia. (Fernando Llano/AP)

On Friday, two civilians were killed and 11 wounded after the Venezuelan military opened fire on protesters near the Brazilian border.

Also on Friday, Guaidó had defied a travel ban and left Venezuela, crossing into Colombia to make a surprise appearance in the city of Cucuta.

There, Guaidó appeared at “Venezuela Aid Live,” a star-studded benefit concert in support of the opposition party, sponsored by British billionaire Richard Branson.

The event was planned in three weeks and intentionally located on the Colombian side near the Tienditas International Bridge, where blockades were preventing humanitarian aid from entering Venezuela.

“There aren’t many things that I am willing to miss a Virgin Galactic spaceflight for — but I really wanted to show my support for the people of Venezuela,” Branson wrote on his blog. “It really was a momentous day and the world can no longer close its eyes to this unacceptable situation.”

True to form, Branson also later tweeted an image of what the massive concert crowd looked like from space.

Dylan Baddour, Anthony Faiola, Mariana Zuñiga and Maite Fernandez contributed to this report.

Read more:

Venezuela’s crisis: How did it get so bad?

A historic exodus is leaving Venezuela without teachers, doctors and electricians

Venezuela’s crisis in 5 charts

The accidental leader: How Juan Guaidó became the face of Venezuela’s uprising

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