President Trump has said he prefers a peaceful transfer of power, but assured all options are on the table.
After the Brazilian government pledged to also send aid in, Maduro declared that the Venezuelan government would close the border with Brazil on Thursday night.
"This is the real humanitarian aid of Venezuela", said Ramirez.
Maduro's government is suspicious of the USA stated plan to provide humanitarian assistance to Venezuelan opposition.
The United States and scores of other countries have openly backed Guaido, who last month invoked constitutional provisions to assume the interim presidency after declaring Maduro's re-election a year ago illegitimate.
Caracas would not allow such aid into the country, Maduro said, saying the country was coping with its difficulties and that U.S. "concerns" over Venezuela's humanitarian crisis were "fabricated by Washington over the last four years to justify intervening in our country".More news: World's biggest bee rediscovered in Indonesia
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The opposition says it is rallying relief efforts in Venezuela to alleviate widespread food and medicine shortages in the wake of its hyperinflationary economic collapse. "There are many people who feel it was a fraudulent election, and I think the United States has got to work with the global community to make sure that there is a free and fair election in Venezuela", Sanders responded.
Besides closing the border with Brazil, Venezuelan Vice President Delcy Rodriguez said the day before that the Latin American country would close the border with neighboring island nations, suspend air traffic and revise their diplomatic ties.
Amnesty International's Americas director Erika Guevara urged authorities to "guarantee access" for those bringing in aid.
"It's part of this calculus that sees the military as leading a transition in Venezuela", said Geoff Ramsey at the Washington Office on Latin America (WOLA), a thinktank.
Underlining the swell of global support for Guaido, British entrepreneur Richard Branson plans to hold a pro-aid concert just inside Colombia on Friday, while Maduro's government stages a rival concert on its side of the border, around 1,000 feet (300 meters) away.