US President Donald Trump has said he recognises Venezuelan opposition leader Juan Guaidó as interim president.
In a statement, Mr Trump described Mr Maduro's leadership as "illegitimate" and said the country's congress was the only "legitimate branch of government" in the country.
It comes amid political turmoil and mass protests against President Nicolás Maduro who has overseen years of economic freefall.
In response to Mr Trump's recognition of the opposition leader, Mr Maduro broke diplomatic ties with the US and gave its diplomatic staff 72 hours to leave Venezuela.
The announcement came minutes after the 35-year-old declared himself acting leader in Caracas on Wednesday.
Hyperinflation, power cuts and shortages of basic items have driven millions of people out of Venezuela.
Mr Maduro was sworn in for a second term earlier this month, after a vote marred by an opposition boycott and widespread claims of vote-rigging.
- Read our Analysis from Michael Hall for more background on why this is happening
- Violent protests yesterday left several people dead, the toll rising from four to 13
Mr Maduro accused Washington of trying to govern Venezuela from afar and said the opposition was seeking to stage a coup.
"We've had enough interventionism, here we have dignity, damn it!" he said in a televised address from the presidential palace.
Some counter-demonstrations are also being held in support of Mr Maduro, but these are reported to be on a much smaller scale.
Earlier on Wednesday, Mr Guaidó told a cheering crowd in Caracas that the protests would continue "until Venezuela is liberated".
"I swear to formally assume the national executive powers as acting president," he said, while raising his right hand.
Mr Guaidó, who is head of the National Assembly, called on the armed forces - who have so far backed Mr Maduro - to disobey the government.
Venezuela's defence minister has condemned Mr Guaidó, who has promised to lead a transitional government and hold free elections.
Mr Maduro has worked hard to keep the military leadership on his side, giving officers key government posts and offering lucrative oilfield services contracts to military-linked firms.
Some 13 people had been killed during Wednesday's protests, the rights group the Venezuelan Observatory of Social Conflicts said.
Mr Trump said the US would hold Mr Maduro's regime "directly responsible" for any threats to the safety of the Venezuelan people.
"The people of Venezuela have courageously spoken out against Maduro and his regime and demanded freedom and the rule of law," his statement said.
He also urged other nations to follow suit in supporting Mr Guaidó.
So far, seven South American countries - Brazil, Colombia, Chile, Peru, Ecuador, Argentina and Paraguay - have done so, however Mexico, Bolivia and Cuba have expressed support for Mr Maduro.
Canada has also given its backing to Mr Guaidó, while European Council President Donald Tusk said he hoped the EU would "unite in support of democratic forces".
US secretary of state Mike Pompeo also rejected Mr Maduro's move to cut ties with the US, saying that the US did not recognise him as leader and would instead conduct relations "through the government of interim President Guaidó".
Mr Pompeo urged Venezuela's military to support efforts to restore democracy and said the US would back Mr Guaidó in his attempts to establish a government.