Venezuelan opposition leader Juan Guaido urged the military to defy the acting president's orders and let Saturday's planned delivery of US-supplied humanitarian aid go ahead smoothly.

Tensions were running high at the financially crippled country's borders with Brazil and Colombia, where stockpiles of food and medical kits have been waiting to enter.

Acting President Nicolas Maduro insists there is no humanitarian crisis in Venezuela. He has sought to block efforts to bring in aid, calling them part of a US-backed ploy to topple him from power.

Read more: Opinion: A new Cold War in Venezuela?

The socialist leader has shut the southern frontiers with Brazil and Colombia. He's also ordered the military to turn away aid convoys — setting the stage for a possible confrontation when the opposition attempts to carry out its deliveries on Saturday.

"You must decide which side you are on in this definitive hour," Guaido, who last month declared himself interim president, wrote on Twitter. "To all the military: between today and tomorrow, you will define how you want to be remembered."

Violence at the border

The army, who has so far remained loyal to Maduro, killed two people from an indigenous community near the Brazilian border on Friday after they stopped a military convoy that they believed was tasked with blocking aid, according to local leaders.

"I stood up to them to back the humanitarian aid," one of the leaders, Richard Fernandez, told Reuters news agency. "And they came charging at us. They shot innocent people who were in their homes, working."

Maduro's allies accused the community of forming "violent groups" and acting on the orders of the opposition.

UN Secretary-General Antonio Guterres on Friday urged "the Venezuelan authorities not to use lethal force against demonstrators."

Read more: Venezuela's health care crisis: Hospitals have 'nothing left'

US planes bringing some 200 tons of aid for Venezuela land at Cucuta in Colombia

According to the UN, some 2.7 million people have fled Venezuela since 2015. A growing number of the country's population are suffering from malnutrition after years of severe food and medicine shortages.

Guaido — who has been recognized as the legitimate president by more than 50 countries — has vowed to start delivering on Saturday the tons of foreign aid amassed at the Colombian border city of Cucuta, Boa Vista on Brazil's border and the Dutch Caribbean island of Curacao.

Russia and China, which both support Maduro, warned that forcing humanitarian aid across the border could provoke violent clashes.

Counter concerts

Nearly 200,000 people attended a Live Aid-style concert in Cucuta, Colombia, late Friday to pressure Maduro to open the borders to aid.

On the other side of the border, Maduro himself put on a much smaller rival concert under the slogan "Hands Off Venezuela."

Guaido defied a government-issued travel ban to attend the Colombian event, which was organized by British billionaire Richard Branson.

"The people of Venezuela are not begging, they're resisting a dictatorship, the onslaught of oppression," Guaido told a news conference after the concert. "Tomorrow ... everyone will be on the streets demanding the entry of humanitarian aid."

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