Venezuela's dire situation has fuelled a political crisis that has peaked over the last month with Guaido invoking a constitutional provision to declare himself the legitimate, interim president. But the aid blockade could lead to troops disobeying Maduro's orders and allowing the much-needed aid to pass.
Maduro argues Venezuela isn't a nation of "beggars" and has long rejected receiving humanitarian assistance, equating it to a foreign intervention.
The pro-Maduro Supreme Court has already barred Guaido from leaving the country and frozen his bank accounts while prosecutors investigate what they call his anti-government activities.
"We do not agree with the content of the document", Maduro said.
Despite growing global political support for the opposition, the Venezuelan military has not defected en masse, and it remains unclear where the USA and the opposition go from here.
Opposition leader Juan Guaido, who requested the global assistance, said it is necessary in a country racked by shortages of basic goods.
He also hit out at European and Latin American ministers who called for a new presidential ballot.
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In Caracas, President Nicolas Maduro denounced the presence of trailers of humanitarian aid brought to the Colombian border, calling them part of a plan cooked up in Washington to destabilize his government.
But a USA military intervention in Venezuela could fracture support from Latin American counties that have been critical of past US interventions in the region and could bolster Maduro's image in Venezuela as a sympathetic and anti-imperialist leader.
At the request of Interim President Juan Guaidó, the United States is immediately pre-positioning emergency supplies in Colombia to provide relief to Venezuelans coping with severe food and medicine shortages.
"The aid is going to be backed by popular support, by hundreds and thousands of people who need it", he said.
Despite the warning, U.S. and Colombian officials have said they do not plan to use military force to get tens of millions of dollars of humanitarian aid into Venezuela. Maduro has consistently denied that a humanitarian crisis is happening in the country, blaming food and medicine shortages on the U.S. sanctions, which have mostly targeted individuals and the state-owned oil company.
General Francisco Yanez of the air force's high command became the first active Venezuelan general to recognise Guaido, but he is one of about 2,000 generals. "Venezuela is not suffering the humanitarian crisis made up by Washington over the last four years to justify intervening in our country".
He said the aid should be given to the poor in the Colombian city of Cucuta, where the supplies are being stockpiled.
Guaido warned military officers against blocking the arrival of aid amid spiralling disease and malnutrition brought on by a hyperinflationary collapse. They aim for "a peaceful solution and dialogue favorable for Venezuela". He was arrested last month after he entered Venezuela clandestinely from Colombia. "While we work every day to reach the delivery of humanitarian aid, they insist in siphoning the medicines and food from those who urgently need it".