Caracas: On Saturday, a high-risk opposition campaign to deliver humanitarian aid into Venezuela descended into chaos after President Nicolas Maduro's security forces fired on demonstrators and aid trucks were set ablaze as his blockade held firm. Two people, including a 14-year-old boy, were killed in clashes with security forces on the Brazil-Venezuela border amid efforts to bring in aid there, a human rights group said. However, opposition leader Juan Guaido had set a Saturday deadline for the delivery of food and medical aid stockpiled in Colombia and Brazil. Aid is also being held on the Caribbean island of Curacao because of Maduro's ban. But hundreds of volunteers, many clad in white, were frustrated in their attempts to collect the aid at the Colombian border, pinned back by Maduro's security forces. Since dawn, protesters in the border towns of Urena and San Antonio were held at bay by the Venezuelan National Guard firing tear gas and rubber bullets. also read US Democrats aim to block President Donald Trump for construction of his controversial southern border wall Gunshots could be heard in the streets of Urena during hours of rioting. Maduro's supporters halted and set ablaze two trucks loaded with aid driven through barricades on a border bridge, sending a pall of black smoke into the sky over the Santander crossing linking Cucuta, Colombia with Urena, Venezuela. Opposition lawmaker Gaby Arellano told reporters "People are saving the bulk of what's on the first truck, and looking after the humanitarian aid that Maduro the dictator ordered burned,". Guaido said "The humanitarian aid is definitely going to Venezuela in a peaceful and calm manner to save lives at this time,". Guaido said from Cucuta, Colombia, where he was coordinating the delivery of aid "Our brave volunteers are making a chain to safeguard food and medicines, the humanitarian avalanche is unstoppable,". Some National Guard troops took advantage of the confusion to abandon their posts and cross into Colombia. Colombia's immigration service said at least 23 members of the security forces -- 20 of them troops -- had deserted by Saturday afternoon. Guaido, recognized as an interim leader by more than 50 countries -- said they would be welcomed and not treated as traitors. The opposition leader formally launched a long-planned distribution operation at a warehouse at the Tienditas border bridge in Cucuta joined by the presidents of Chile, Colombia and Paraguay. also read At ISSF World Cup Indian shooter Apurvi Chandela clinching a gold medal Shortly afterwards, he claimed a first shipment had reached Venezuela to defy Maduro's blockade. But the truck he was referring to remained stuck at the Brazilian border hours later. Guaido has vowed humanitarian aid would enter his country despite the blockade.His supporters planned to drive the aid from Colombia into Venezuela at the closed border crossings supported by a flood of volunteers and accompanied by Catholic priests in an attempt to avoid arrest. Socialist leader Maduro has rejected the aid, which he's dismissed as a show and pretext for a US invasion. Angered by Colombia's support for Guaido, Maduro announced Venezuela was severing diplomatic ties with Bogota.