The UK, France, Germany, Spain and other European countries have officially recognised opposition leader Juan Guaidó as interim president of Venezuela.
It comes after President Nicolás Maduro defiantly rejected the EU's Sunday deadline to call snap elections.
Mr Guaidó declared himself interim leader last month and won US backing.
Russia – a backer of Mr Maduro – accused EU countries of meddling in Venezuela's affairs.
As pressure mounted on Mr Maduro to step down, he said he could not rule out the possibility of civil war.
In a TV interview, he warned that US President Donald Trump would leave the White House "stained with blood" if he intervened in the crisis.
Mr Guaidó said on Sunday he would build an international coalition to deliver humanitarian aid to Venezuelans.
What have EU countries said?
Sunday saw the expiry of an ultimatum set by several European countries – including France, the UK, Austria, Germany and Spain – for Mr Maduro to call early presidential elections. They said that they would recognise Mr Guaidó as interim president if no such pledge was forthcoming.
On Monday, the UK, Spain, Denmark, Austria, France and Sweden officially recognised Mr Guaidó as interim president.
"UK alongside European allies now recognises @jguaido as interim constitutional president until credible elections can be held", Foreign Secretary Jeremy Hunt said in a statement on Twitter.
French President Emmanuel Macron said Venezuelan's had the right to "express themselves freely and democratically", calling on Mr Guaidó to organise a fresh presidential poll. He announced his support for an EU contact group in the interim.
Spain's Prime Minister Pedro Sanchez urged him to call elections "as quickly as possible."
"Venezuela should be the author of its own destiny. The international community has a duty to help and ensure that this happens with the necessary guarantees", he told reporters.
But Russia slammed the statements, accusing EU countries of interfering in the Venezuela's affairs and attempting to "legitimise usurped power".
What did Maduro say?
Mr Maduro responded to the EU's deadline saying: "We don't accept ultimatums from anyone. It's like if I told the European Union: 'I give you seven days to recognise the Republic of Catalonia, and if you don't, we are going to take measures'.