"We will return to the streets.to demand the entry of humanitarian aid that will save the lives of more than 300,000 Venezuelans that today are at risk of dying", Guaido said on Twitter late Monday.
For his supporters, Guaido appeared to be something of a rockstar, as they desperately tried to take selfies and cheered emphatically every time he spoke or his name was mentioned.
Guaido, recognized by the USA and some 50 other countries as the interim president of Venezuela, spoke Tuesday to thousands of supporters who demonstrated as part of an ongoing campaign to break the military's support for Maduro and force the socialist leader from power.
Foreign Minister Enzo Moavero Milanesi said the 2018 election was "invalidated in their correctness, fairness and legality", leaving Maduro without "democratic legitimacy" as president.
"The Ku Klux Klan governing the White House today wants to take possession of Venezuela", he said.
"He is, publicly and openly".
Maduro is expected to lead a march of his own in Caracas, protesting what he has called "imperialist intervention" by the United States and other foreign governments. He urged Washington to lift sanctions it has imposed on the country and free up funds it has frozen in USA and foreign banks.
"This is part of that charade".
He said he will reject the "minuscule crumbs that they intend to bring with toxic food, with leftovers that they have".More news: ‘Apex Legends’ Is Replacing ‘Fortnite’ as the King of Battle Royale Games
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Foreign Secretary, Jeremy Hunt, said the United Kingdom believes Mr Guaido is Venezuela's interim president.
Most Western counties including the United States have recognized Guaido as Venezuela's president, but Maduro retains the backing of Russian Federation and China as well as control of state institutions including the military.
"What's the logic, reasoning, to repeat an election?" he asked.
While the United Nations, the government in Caracas and many Latin American and Caribbean countries are committed to dialogue, the Venezuelan opposition led by Juan Guaido -head of a parliament in contempt and who was self-declared "interim president"- rejects that option and seeks USA support.
Maduro also rallied supporters at rival demonstrations following more than a month of pressure, with National Guard members dressed in riot gear blocking some streets in anticipation of opposition demonstrators.
The US is sparking a war to seize Venezuela, he said, highlighting that "Venezuela is a country that has the capacity to satisfy all the necessities of our people" and that "our people do not to beg from anyone".
Guaido vows to deliver it to Venezuelans who need it, but his strategy for outmanoeuvring Maduro remains unclear.
The aid is still stranded on a key bridge linking Venezuela with Colombia, blockaded by Maduro's forces.
"There are many Venezuelans in Israel and many Jews in Venezuela", Guaido said.
Prada, a 24-year-old mother of two, said she left home in Venezuela last week after her 2-year-old son came down with a odd rash and she wasn't able to get treatment.