Support from the Venezuelan military is "crucial" to efforts to oust President Nicolas Maduro, opposition leader Juan Guaido wrote in The New York Times on Wednesday.
Mr Guaido said that secret meetings had been held with members of the security forces, and that most of those in uniform agree that the status quo cannot continue.
"The military's withdrawal of support from Mr Maduro is crucial to enabling a change in government, and the majority of those in service agree that the country's recent travails are untenable," Mr Guaido wrote.
"The transition will require support from key military contingents. We have had clandestine meetings with members of the armed forces and the security forces."
White House spokeswoman Sarah Sanders tweeted a link to Mr Guaido's op-ed along with the message: "America stands with the people of Venezuela."
Venezuela – which has the world's largest proven oil reserves – has suffered an economic meltdown under Mr Maduro's leadership, marked by hyperinflation and shortages of basic necessities such as food and medicine.
Millions have been left in poverty, while 2.3 million more have fled the country, unleashing a migration crisis in South America.
Mr Guaido declared himself interim president last week, arguing that Mr Maduro's re-election was illegitimate and that he, as president of the National Assembly, was constitutionally mandated to step in.
He quickly earned the support of the United States and several Latin American countries, and six major European nations have told Mr Maduro to call fresh elections by the weekend or they too will recognise his opponent.
European Union foreign ministers are expected to discuss their stance on Venezuela at a meeting in Bucharest on Thursday. British Foreign Secretary Jeremy Hunt said before the meeting that he would propose sanctions against members of the Maduro regime to pressure the Venezuelan leader into calling fresh elections.
"We are not considering sanctions against the whole country because there is a humanitarian situation and we wouldn't want to make the situation even worse," Mr Hunt said in a statement.
"But targeted sanctions against the kleptocrats who have enriched themselves on the back of the rest of the population who are very poor, that is something I think can be effective."
Meanwhile, Spain has demanded the release of three journalists from the state-run EFE news agency who were arrested in the Venezuelan capital on Wednesday.
EFE reported that Colombian photographer Leonardo Munoz disappeared on Wednesday morning in Caracas and that two more reporters, Spaniard Gonzalo Dominguez and Colombian Mauren Barriga, were later taken away from their office by members of Venezuelan intelligence service Sebi.
Spain's government said a Venezuelan driver working for the news agency was also taken into custody.