Venezuela’s opposition leader Juan Guaidó has held secret meetings with the military to win support for ousting President Nicolás Maduro.
Mr Guaidó made the revelation in a New York Times opinion piece.
The opposition leader declared himself interim president earlier this month, prompting an escalating power struggle.
Russia and China continue to back Mr Maduro, while the US and several Latin American countries have recognised Mr Guaidó.
US President Donald Trump tweeted on Wednesday that he had spoken to Mr Guaidó and supported his “historic assumption of the presidency”, writing in a second tweet that “The fight for freedom has begun!”
UK Foreign Secretary Jeremy Hunt meanwhile is expected to urge EU nations to impose sanctions on key figures in Mr Maduro’s government on Thursday, after also speaking to Mr Guaidó on Wednesday.
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About three million people have fled Venezuela amid acute economic problems, and there has been an upsurge in violence in recent weeks.
Protests have been held across the country since Mr Maduro began his second term on 10 January. He was elected last year during a controversial vote in which many opposition candidates were barred from running, or jailed.
What did Mr Guaidó’s piece say?
“We have had clandestine meetings with members of the armed forces and the security forces,” Mr Guaidó writes in the New York Times article.
“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.”
The article also says the opposition has offered an amnesty to armed forces “found not guilty of crimes against humanity”.
As head of Venezuela’s National Assembly, Mr Guaidó says the constitution allows him to assume power temporarily when the president is deemed illegitimate.
Venezuela’s Supreme Court has banned the opposition leader from leaving the country, however, and frozen his bank accounts.
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Mr Guaidó’s piece comes the same day as fresh protests began against Mr Maduro.
Venezuela’s president earlier told Russian news agency RIA he was prepared to hold talks with the opposition “so that we could talk for the good of Venezuela”.
He added that he was not prepared to accept ultimatums or blackmail, and insisted that he has the backing of Venezuela’s military, accusing deserters of conspiring to plot a coup.
What’s the reaction to the crisis?
The US and more than 20 other nations have backed Mr Guaidó.
On Monday, the US imposed curbs on the country’s state-owned oil firm PDVSA.
US National Security Adviser John Bolton spoke to businesses via Twitter on Wednesday, telling them not to deal in “gold, oil, or other Venezuelan commodities” stolen from the people by “the Maduro mafia”.
Mr Maduro has the backing of Russia, China, and Turkey.
Russian officials have denied reports that mercenaries from the country have been sent to protect his life.
Mexico and Uruguay meanwhile have announced plans for a conference of “neutral” countries on 7 February in Uruguay’s capital Montevideo, to discuss the crisis.
Diplomatic pressure grows
By James Landale, BBC diplomatic correspondent
European leaders have already warned that if Mr Maduro does not announce fresh elections by Sunday, then they will join the United States and others in formally recognising the opposition leader, Juan Guaido, as interim president.
On Thursday, at a meeting in Romania, UK Foreign Secretary Jeremy Hunt will urge his EU counterparts to go further, and consider imposing sanctions on key figures within the government.
That would not be easy, requiring unanimous EU support, but the foreign secretary believes it should be considered.
The EU has an existing sanctions regime against 18 Venezuelans accused of human rights abuses and this list could be extended.
Mr Guaido, who spoke to Mr Hunt on Wednesday, is understood to be urging the EU to take a tougher action against the government in Caracas.
US officials have previously stated that all options “are on the table” to resolve the crisis in Venezuela, which observers have taken to include possible military action.
Mr Bolton also appeared at a news briefing with a notepad showing the words “5,000 troops to Colombia”, which borders Venezuela.
The Lima Group – a 14-country body including Canada set up in 2017 to find a peaceful solution to the crisis – has opposed any military intervention in the country.