CÚCUTA, Colombia — Waving banners and chanting slogans against their government, supporters of Venezuela’s opposition prepared to defy President Nicolás Maduro on Saturday and make good on their promise to break his humanitarian aid blockade along the country’s multiple borders.
Already, the conflict had turned deadly. On Friday, security forces opened fire on a crowd blocking access to a road, killing two people and injuring a dozen others. It raised fears that more bloodshed could follow on Saturday as more confrontations ensued.
As evening fell on Friday, Mr. Maduro’s government added three bridges at the Colombian border to a growing list to border closures that included Brazil and three Caribbean islands, effectively sealing off most of Venezuela’s main entry points by land and sea.
But a Venezuelan official also hinted that the government might be easing its hard-line stance. Diosdado Cabello, a top official in the ruling party, said that if some Venezuelans entered with aid in their hands, “nothing would happen” to them.
As the sun rose on 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 Mr. Maduro.
“I know it’s been a long night but we are moving ahead,” an opposition member, Adolfo Marin, 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 only eats just one meal a day. They have a sister that can’t get medicine for her illness.”
The border showdown has become one of the most tense and unusual in the region’s history.
Juan Guaidó, the leader of the opposition, claims to be Venezuela’s rightful leader and has been recognized as such by more than 50 countries, including the United States. He has staked his challenge to Mr. 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 Mr. Maduro or “lose everything.” In response to the killings on Friday, the White House issued a statement strongly condemning the use of force by Mr. 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.
Mr. Maduro now alleges 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.
Before the border closure, Mr. Guaidó himself slipped in over the border into Colombia, where he attended a Latin pop music concert in support of the opposition that was sponsored by the British billionaire Richard Branson. Mr. Guaidó was greeted like a rock star, with cheers and denunciations of Mr. Maduro.
Mr. Guaidó was expected to be among those leading the march over the bridge. But it was unclear whether the authorities would allow him into the country or arrest him for defying a travel ban that Mr. Maduro’s government had imposed.
Some Colombians expressed sympathy with Mr. 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 were suffering from 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 suffered 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.”
More recently, he said, “we ate once, sometimes twice, daily. This after living peacefully with three normal meals a day and sometimes a snack or a stew on Sunday. We just had nothing.”