Three members of Venezuelan President Nicolás Maduro’s inner circle agreed with the opposition that he “had to go”, but then backtracked, US officials have said.
It comes after the opposition leader Juan Guaidó called on the military to help him end Mr Maduro’s rule.
Protesters took to the streets in the capital Caracas in support on Tuesday.
But military leaders appeared to be standing behind Mr Maduro, accusing Mr Guaidó of an attempted coup.
Mr Bolton offered no evidence that Mr Maduro’s loyalists were preparing to abandon him. The assertions were later repeated by Elliott Abrams, the US envoy for Venezuela.
Venezuela’s Defence Minister Vladimir Padrino appeared on television surrounded by soldiers, asserting their support for Mr Maduro as protesters demanded he step down.
However, according to the US National Security Advisor John Bolton, Mr Padrino was one of the men involved in three months of negotiations with the opposition.
He also named Supreme Court chief judge Maikel Moreno and presidential guard commander Ivan Rafael Hernandez Dala.
Mr Bolton said they had committed to “to achieve the peaceful transition of power from the Maduro clique” to Mr Guaidó, who the US, UK and a number of the other countries recognise as Venezuela’s rightful leader.
“All agreed that Maduro had to go,” Mr Bolton told reporters in Washington.
What’s happening in Venezuela?
This morning Mr Guaidó appeared alongside another opposition leader, Leopoldo López, who had been under house arrest since being found guilty of inciting violence during anti-government protests in 2014, in a three-minute video.
In it, he declared he was in the “final phase” of ending President Maduro’s rule and announced he had the support of “brave soldiers” in Caracas.
“The National Armed Forces have taken the correct decision… they are guaranteed to be on the right side of history,” he said.
However, the entire military did not appear to be backing Mr Guaidó as the morning continued.
The BBC’s Guillermo Olmo, in Caracas, said Tuesday marked the most violent episode of the Venezuelan political crisis so far.
There were running clashes between Mr Guaidó’s supporters and armed military vehicles. Protesters were also seen throwing rocks, but being repelled by tear gas and water cannon.
Television cameras also caught the moment armoured vehicles drove into a crowd but it is unclear if there were any injuries in that incident.
Venezuela’s health ministry said 69 people had been injured across the country.
Read more about Venezuela’s crisis:
Mr Padrino appeared on the television saying the uprising by some members of the military had been “partly defeated”, but warned of possible bloodshed.
“The weapons of the republic are here to defend the nation’s sovereignty and independence,” he warned.
He also revealed one soldier had suffered a bullet wound.
By the end of the day, Mr López, who leads the Popular Will party of which Mr Guaidó is a member, his wife Lilian Tintori and their daughter had entered Chile’s embassy in Caracas to seek protection, Chile’s Ministry of Foreign Affairs said.
A failure, or more to come?
by Katy Watson, BBC News
Tuesday’s events have definitely been dramatic. But it’s not clear where it leaves Venezuela.
Juan Guaidó made a bold move by saying the armed forces were on his side early in the morning. And the fact that opposition politician Leopoldo López, who was under house arrest, stood beside him was also big surprise. Who had freed him and what did that say about the loyalties of the armed forces?
But as the day went on, little clarity emerged – who exactly is behind this so-called uprising? For Juan Guaidó to achieve the regime change he’s promised, he needs the generals at the top on his side. So far though, at least publicly, they remain loyal to Mr Maduro.
The situation on the ground is still confusing – but the confidence that the opposition had at the beginning of the day looks like it’s waning.
Leopoldo López and his family are now ‘guests’ at the Chilean residence in Caracas – is that a sign that once again, the opposition’s attempts to take power have failed, or is there another dramatic twist to come?