Venezuela's opposition leader Juan Guaidó says he has held secret meetings with the military to win support for ousting President Nicolás Maduro.
Mr Guaidó declared himself interim president earlier this month and was immediately recognised by the US and several Latin American countries.
Major powers Russia and China back Mr Maduro and military support is seen as crucial to his hold on power.
The crisis comes as Mr Maduro began a second term after controversial polls.
Many opposition candidates were barred from running or jailed.
About three million people have fled Venezuela amid acute economic problems, and there has been an upsurge in violence in recent weeks.
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.
What did Mr Guaidó say?
"We have had clandestine meetings with members of the armed forces and the security forces," Mr Guaidó writes in an article in the New York Times.
"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".
However Mr Guaidó did not say who in the military he had been speaking with or what their positions were.
Venezuela's top military representative to the US Col José Luis Silva has defected - but senior military figures in Venezuela have supported Mr Maduro.-BBC
