Guaido's international backers are using a mix of sanctions and diplomacy to try to put pressure on Maduro.
Venezuelan military officials last weekend blocked an opposition-backed effort to bring food into the country via its borders with Colombia and Brazil, leaving two aid trucks in flames and five people dead.
Guaido, who is recognised by most Western nations as Venezuela's rightful leader, visited Paraguay and Argentina on Friday to shore up Latin American support for a transition government for the crisis-stricken nation.
But Maduro retains control of state institutions and the loyalty of senior figures in the armed forces.
Following a meeting with Argentine President Mauricio Macri in Buenos Aires, Guaido said, without providing evidence, that 80 percent of Venezuela's military nonetheless supported a change in leadership and that he would continue to seek the support of officers.
Earlier on Friday in Paraguay, he said 600 members of Venezuela's armed forces had already abandoned Maduro's government following the clashes over the aid.
Some analysts agree with Guaido's assessment.
"The impoverishment and the crisis in Venezuela is so acute, that there is a rejection within the armed forces towards the government, particularly in the middle and lower ranks," Sebastiana Barraez, a journalist and an expert on Venezuela's military forces.
Foreign military intervention is seen as unlikely and Guaido's international backers are instead using a mix of sanctions and diplomacy to try to put pressure to bear on Maduro.
"We are sanctioning members of Maduro's security forces in response to the reprehensible violence, tragic deaths, and unconscionable torching of food and medicine destined for sick and starving Venezuelans," US Treasury Secretary Steven Mnuchin said in a statement on Friday.
The US "will continue to target Maduro loyalists prolonging the suffering of the victims of this man-made humanitarian crisis," he said.
US sanctions block any assets the individuals control in the US and bars US entities from doing any business or financial transactions with them.
The US State Department also said it had revoked the travel visas of 49 people as it cracked down on "individuals responsible for undermining Venezuela's democracy."
Maduro says the US is trying to destabilise his country and that efforts by the US-backed opposition to bring aid into the country are a political theatre.
"[For our] Dignity, we will fight harder than ever," the president said during a rally.
"[The] days will go by, weeks will go by and Nicolas Maduro the worker's president will continue at the head of the motherland."
Guaido slipped out of Venezuela last week, in violation of a Supreme Court order not to leave the country, to join the aid convoys in Colombia. There, he met US Vice President Mike Pence and other regional leaders and later travelled to Brazil.
He has promised to return to Venezuela by Monday, seen as a form of direct defiance to Maduro, who has said Guaido will eventually "face justice".
The Argentine foreign ministry said in a statement that it expects the peaceful and safe return of the opposition leader to Venezuela, without risk to him, his family or his supporters.
Paraguayan President Mario Abdo tweeted on Friday evening that he authorised expired Venezuelan passports to be valid in Paraguay, a gesture of support for Venezuelans who have fled their home country.
Guaido also called for further protests upon his return.
"We can't allow a regime that openly violates human rights and blocks international aid, to feel that it can go unpunished," he said after meeting Argentinian President Macri in Buenos Aires.