The US ambassador to Bolivia has been ordered to leave the country by President Evo Morales.
Mr Morales accused Philip Goldberg of "conspiring against democracy" and encouraging the country's break-up.
A US state department spokesman said it had received no formal word of the dismissal and described the accusations against Mr Goldberg as "baseless".
Bolivia has seen large protests in recent weeks by opponents of Mr Morales' economic and social policies.
"The ambassador of the United States is conspiring against democracy and wants Bolivia to break apart," Mr Morales said, in a speech at the presidential palace in La Paz.
The president said the foreign minister would inform Mr Goldberg that he "should return to his country at once".
Mr Morales did not say what evidence he had to support his allegation but claimed to have the government's backing.
The US embassy on its website said that Mr Goldberg was in a meeting with the Bolivian Foreign Minister, David Choquehuanca, when he was informed that President Morales had declared him persona non grata.
The statement said Mr Goldberg was surprised at Mr Morales' "sudden decision" and that the embassy was waiting for an official diplomatic communication, as required by the Vienna Convention on Diplomatic Relations.
The announcement comes after several weeks of demonstrations by groups opposing Mr Morales.
Protesters have been blocking roads and occupying buildings in eastern regions, which are home to Bolivia's important natural gas reserves.
Opposition groups want a greater autonomy as well as more control over revenues of natural gas in their areas.
They object to Mr Morales' plans to give more power to the country's indigenous and poor communities, by carrying out land reform and redistributing gas revenues.
Earlier this week, the government announced it was sending the military to protect gas fields and infrastructure from demonstrators and guarantee exports to neighbouring countries.
On Wednesday, officials said saboteurs had caused a blast on a pipeline, forcing them to cut natural gas exports to neighbouring Brazil by 10%.
The Brazilian foreign ministry said in a statement that the government was taking the necessary measures to guarantee gas supplies in the country.
The statement also expressed Brazil's "grave concern" at the events in Bolivia, and deplored the outbreak of violence and attacks on state institutions and public order.