By Agence France-Presse Venezuela's opposition leader Juan Guaido claimed the military helped him defy a travel ban by the government of President Nicolas Maduro as he joined thousands over the Colombian border on Friday for a charity concert to push for humanitarian aid deliveries. Maduro is trying to prevent food and medicines, mainly from the US, from entering the country as tensions over access to the supplies turned deadly elsewhere. Thousands wait for the start of the Venezuela Aid Live concert in Cucuta, Colombia (AFP Photo/RAUL ARBOLEDA / MANILA BULLETIN) Humanitarian aid has become a key focus of the power struggle between Maduro and Guaido, who has been recognized as interim leader by more than 50 countries. Guaido delivered a blow to Maduro as he turned up unexpectedly at the concert in the Colombian border town of Cucuta, claiming "the armed forces participated in this process" to help him flout his travel ban. The powerful military's backing is crucial to the viability of the socialist leader, with defections strengthening Guaido's hand. The 35-year-old leader of Venezuela's National Assembly declared himself interim president last month and is calling for fresh polls, branding Maduro a "usurper" and accusing him of rigging his re-election last May. 'Soldiers started shooting' The tense standoff over aid meanwhile claimed its first casualties Friday as two indigenous people were killed trying to prevent troops from sealing unofficial pathways across the Brazilian border. "An indigenous woman and her husband were killed and at least 15 other members of the Pemon indigenous community were injured," said a local human rights group, Kape Kape. The violence occurred in southeastern Bolivar state close to the border with Brazil, which Maduro ordered closed on Thursday. Guaido called on the military to arrest those responsible for the killings, "or you will be responsible." "It wasn't a clash, it was an attack," said Salomon Perez, who accompanied a brother and two nieces suffering from gunshot wounds by ambulance to a hospital in Brazil. "People were in their community, calm. The soldiers came and started shooting at the indigenous people," he said from Roraima state in northern Brazil. United Nations Secretary-General Antonio Guterres issued a stern statement, warning Venezuelan authorities "not to use lethal force against demonstrators." - Fleeing shortages - The "Venezuela Aid Live" concert in Cucuta was organized by British entrepreneur Richard Branson in support of Guaido's humanitarian aid relief plan. Guaido appeared alongside Colombian President Ivan Duque, Chile's Sebastian Pinera and Mario Abdo of Paraguay as crowds cheered. A rival pro-Maduro concert was taking place a few hundred yards away on the Venezuelan side of the border in Urena. Guaido has set a Saturday deadline for the entry of humanitarian aid, saying as many as 300,000 Venezuelans are in dire need of food and medicines after years of shortages and malnutrition. Some 2.7 million people have fled Venezuela since 2015 amid a devastating political and economic crisis, according to UN figures released Friday. Maduro, who retains the support of allies China and Russia, has blocked the entry of aid and accused the United States of plotting a military intervention. US special representative Elliott Abrams kept up the foreign pressure on Maduro on Friday, joining a Cucuta-bound plane carrying medical supplies and food. "The humanitarian and the social-economic situation in Venezuela is very bad, there's a terrible need for food, for supplies, and the international community is responding," Abrams said. Moscow has blasted Washington for using aid as a "convenient pretext for conducting military action." 'Freedom' Hundreds chanted "freedom" and "the government is going to fall" while they waited for the Cucuta concert to begin under a hot sun, with the barricaded border crossing visible nearby. "We must break the impasse, end the humanitarian crisis," billionaire Branson told the crowd shortly before veteran Venezuelan crooner Jose Luis Rodriguez began his set. Branson said he hopes to raise $100 million for humanitarian aid over the next 60 days via internet donations, though meanwhile aid is being stockpiled in Colombia, Brazil and the Caribbean island of Curacao because of Maduro's ban. The line-up included Latin American giants Carlos Vives and Juanes of Colombia, Juan Luis Guerra of the Dominican Republic and Puerto Rico's Luis Fonsi. "The concert is an immense help because this type of initiative was necessary to open our eyes and pressure the Venezuelan government," said Wendy Villamizar, a 32-year-old Venezuelan woman wearing a cap with her country's yellow, blue and red tricolor. Maduro's rival concert, decidedly smaller and featuring Venezuelan and Cuban artists, began hours later. Performers took to the stage against a giant backdrop emblazoned with the words "#Trump Hands off Venezuela," with around 2,500 people in attendance. "We don't want to be interfered with, we don't want to be invaded," said Johana Suarez.