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 are 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.
The European Parliament voted on Thursday in a non-binding resolution to recognise Mr Guaidó as interim president until fresh elections can be called.
The European Parliament has no foreign policy powers but urged the European Union and its member states to follow suit.
Inside Venezuela, there are reports of international journalists being detained. Spanish news agency EFE says three of its journalists are being deported to Colombia.
Two French journalists, working for a TV programme called Quotidien, have also been detained. Two others, from Chile, have already been deported.