The troops abandoned their posts at the Simon Bolivar International Bridge on the Colombia-Venezuela border and requested help from Colombia’s immigration officials. Also Saturday, soldiers with Venezuela’s National Guard fired tear gas and rubber bullets at protesters who were demanding to cross the border at Ureña into Colombia to work, according to a CNN crew that witnessed the scene at the Tienditas Bridge.Workers faced off with the soldiers, chanting, “We want to work!” before being dispersed by the tear gas. Men with shirts covering their faces started throwing rocks toward the guard.These tense scenes played out Saturday, a day after violence broke out at a Venezuelan town near the border with Brazil over aid delivery, leaving two people dead and 17 others injured, local authorities said. Tensions are running high at Venezuela’s borders amid opposition plans to usher aid into the country this weekend in defiance of President Nicolas Maduro’s wishes. Maduro called on Venezuelans to “mobilize” Saturday. “Let’s all take to the streets to defend our independence with conscience and joy,” Maduro said on his official Twitter account. On Friday, a standoff occurred between a local indigenous community and the military over aid delivery near Gran Sabana, on the Brazil-Venezuela border, said the town’s mayor, Emilio Gonzalez. He told CNN the military opened fire on an indigenous group trying to facilitate the passage of aid into Venezuela.Gonzalez said soldiers shot and killed a 34-year-old indigenous Venezuelan woman and injured 17 others. National Assembly member Americo De Grazia said on his official Twitter feed that two people had died. The second victim was an indigenous man, according to De Grazia.Gonzalez said indigenous guards detained 27 Venezuelan military members. Venezuela’s Ministry of Defense told CNN it had no information on the incident.Tensions escalate over aidVenezuelan opposition leader Juan Guaido, who invoked a constitutional provision last month to declare himself acting president, condemned the incident in a tweet Friday, saying such acts by the military “will not go unpunished.”Guaido has been working with a raft of global partners to bring Venezuelans desperately needed food and medical supplies. The White House urged the Venezuelan military to allow aid into the country in a statement Friday.”The United States strongly condemns the Venezuelan military’s use of force against unarmed civilians and innocent volunteers on Venezuela’s border with Brazil,” White House press secretary Sarah Sanders said.”Egregious violation of human rights by Maduro and those who are following his orders will not go unpunished. The United States strongly urges the Venezuelan military to uphold its constitutional duty to protect the citizens of Venezuela. The Venezuelan military must allow humanitarian aid to peacefully enter the country. The world is watching.” The violence came as dueling concerts kicked off on the country’s western border with Colombia, where aid deliveries from the United States have been languishing since Maduro blocked the Tienditas Bridge.The United States has so far delivered batches of relief supplies to a border town in Colombia, including food and hygiene kits, ready-to-use supplementary foods and high-energy biscuits. It’s pledged $20 million to help Venezuela, and other countries including Canada, the UK and Germany have chipped in, too. Earlier this week, Guaido named Saturday as the deadline for the aid to cross the border.But the United States announced Friday preparations to bring aid in through another route. “The US and its partners began pre-positioning additional humanitarian aid for Venezuelans in Boa Vista, Brazil,” the US State Department tweeted. The aid consists of food kits “containing rice, beans, sugar, and salt to feed nearly 3,500 people for 10 days and additional rice to feed an estimated 6,100 people for one month,” a fact sheet from the State Department says.Supporters host rival concertsBritish billionaire Richard Branson sponsored a Live Aid-inspired show Friday in Cucuta, Colombia, featuring Latin American stars such as Colombian musical legends Carlos Vives and Juanes, and reggaeton singer Maluma. Colombian President Ivan Duque, Chile’s Sebastian Piñera and Mario Abdo of Paraguay also joined the crowds.As the aid delivery deadline approaches, the spotlight has been on Cucuta, where shipments of US aid are waiting to be delivered.Maduro staged a rival concert a few hundred meters away on the Venezuelan side of the bridge in Tachira.The beleaguered President, who is facing growing calls to step down, denies that a humanitarian crisis exists in his country and suggests that aid efforts are part of a US plot to orchestrate a coup.CNN’s Jorge Luis Perez Valery reported from Caracas and Claudia Dominguez from Atlanta, while Laura Smith-Spark wrote from London. CNN’s Diana Castrillon, Stefano Pozzebon, Diane Ruggiero, Isa Soares and Eliza Mackintosh contributed to this report.