| 24 Jan 2019, 00:00 | Update : 24 Jan 2019, 08:51
US President Donald Trump has recognised Venezuelan opposition leader Juan Guaidó as interim president.
The announcement came minutes after the 35-year-old declared himself acting leader in Caracas on Wednesday.
Meanwhile, a number of South American countries, including Brazil, Colombia and Peru, have also recognised Mr Guaidó as Venezuela's legitimate president.
It comes amid mass protests against President Nicolás Maduro who has overseen years of economic freefall.
Hyperinflation, power cuts and shortages of basic items have driven millions of people out of Venezuela.
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.
In response to Trump's recognition of the opposition leader, Maduro broke diplomatic ties with the US and gave its diplomatic staff 72 hours to leave Venezuela.
He 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 Maduro, but these are reported to be on a much smaller scale.
Earlier on Wednesday, 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.
Guaidó, who is head of the National Assembly, called on the armed forces - who have so far backed Maduro - to disobey the government.
But Venezuela's defence minister has condemned Guaidó, who has promised to lead a transitional government and hold free elections.
The BBC's Latin America Editor Candace Piette says 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.
In a statement, Trump described Maduro's leadership as "illegitimate"and said the country's congress was the only "legitimate branch of government" in the country.
"The people of Venezuela have courageously spoken out against Maduro and his regime and demanded freedom and the rule of law," his statement said.
The statement also said the US would hold Maduro's regime "directly responsible" for any threats to the safety of the Venezuelan people.
Secretary of State Mike Pompeo rejected 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".
Pompeo urged Venezuela's military to support efforts to restore democracy and said the US would back Guaidó in his attempts to establish a government.
A senior US official also said "all options are on the table" and suggested tougher sanctions could be imposed on Venezuela.
In the announcement, Trump also urged other nations to follow suit in supporting Guaidó.
So far, seven South American countries - Brazil, Colombia, Chile, Peru, Ecuador, Argentina and Paraguay - have done so.
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".
But Mexico, Bolivia and Cuba have expressed support for Maduro.
The Organization of American States (OAS) has also recognised Mr Guaidó as president.
"Our congratulations to @jguaido as acting President of #Venezuela," Secretary General Luis Almagro said in a tweet.
In 2017 Venezuela announced it would withdraw from the organisation, which aims to aid co-operation across the continent - accusing it of meddling in its internal affairs.