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 militarily in the crisis, over the legitimacy of his re-election last year.
His rival, Juan Guaidó said on Sunday he would build an international coalition to deliver humanitarian aid to Venezuelans.
Sunday saw the expiry of an ultimatum set by European countries including France, the UK, 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, those countries and and several other European nations 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 Venezuelans had the right to “express themselves freely and democratically “, announcing his support for an EU contact group.
German Chancellor Angela Merkel told a news conference in Tokyo that EU countries expected Mr Guaidó to initiate a swift election process.
Spain’s Prime Minister Pedro Sanchez said 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”.
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’.
“No, international politics can’t be based on ultimatums. That was the era of empires and colonies.”
In the interview with Spanish television programme Salvados, broadcast on Sunday, Mr Maduro was asked if the crisis in Venezuela could result in civil war.
“Today no-one could answer that question with certainty,” he said.
“Everything depends on the level of madness and aggressiveness of the northern empire [the US] and its Western allies.
“We ask that nobody intervenes in our internal affairs… and we prepare ourselves to defend our country.”
President Trump has told US broadcaster CBS the use of military force remains “an option” .
But Mr Maduro warned the US leader he risked a repeat of the Vietnam War – in which the US was involved from 1965 to 1973 – if he intervened.
Hundreds of thousands of US soldiers were sent to help fight communist forces in a costly and unsuccessful war which brought domestic civil unrest and international embarrassment.
“Stop. Stop. Donald Trump! You are making mistakes that are going to stain your hands with blood and you are going to leave the presidency stained with blood,” he said.
“Let’s respect each other, or is it that you are going to repeat a Vietnam in Latin America?”
Thousands took to the streets of the capital Caracas on Saturday for protests in support of both President Maduro and Mr Guaidó.
Mr Maduro retains the support of the military, but ahead of the demonstrations Mr Guaidó received a boost when an air force general – Francisco Yanez – became the highest-ranking military official yet to pledge support for him.
Mr Guaidó says he has held private meetings with the military to win support for ousting Mr Maduro. He says he has also reached out to China, one of Mr Maduro’s most important backers.
Mr Guaidó, who is the head of Venezuela’s National Assembly, declared himself president on 23 January.
He says the constitution allows him to assume power temporarily when the president is deemed illegitimate. On Saturday he said protests would continue until his supporters had achieved “freedom”.