Venezuela has detained three United States citizens, two Spaniards and a Czech national over an alleged plot to destabilise the South American nation, a senior government official said.

Venezuelan Minister of Interior Diosdado Cabello said on Saturday that the six were held on suspicion of planning an attack against President Nicolas Maduro and his government.

The arrests come as tensions have skyrocketed in recent weeks between Venezuela and the US, Spain and other Western nations over a disputed Venezuelan election held in late July.

Maduro, who has been in power since 2013, was declared the winner of the vote, but the country’s opposition has said the contest was marred by fraud and that its candidate had defeated the longtime president.

The election results spurred massive opposition protests, leaving more than two dozen people dead and nearly 200 injured.

During a news conference on Saturday, Cabello accused the two detained Spanish nationals of having alleged links to Spain’s secret service and planning the assassination of a mayor.

The pair were detained while taking photographs in the town of Puerto Ayacucho, the minister said.

Spanish media reported that Spain’s government denied this claim.

Cabello also accused three US citizens and a Czech national of involvement in “terrorist” acts, including alleged plans to assassinate Maduro and other officials.

“These groups seek to seize the country’s wealth, and we as a government will respond firmly to any destabilisation attempt,” Cabello said.

He added that about 400 rifles originating in the US had been seized.

A spokesperson for the US State Department told the Reuters news agency that “a US military member” had been detained in Venezuela and that it was aware of unconfirmed reports of two additional American citizens being detained there.

But the State Department said the US was not involved in an attempt to oust Maduro.

“Any claims of US involvement in a plot to overthrow Maduro are categorically false,” the spokesperson said. “The United States continues to support a democratic solution to the political crisis in Venezuela.”

Venezuela recalled its ambassador to Spain this week for consultations and summoned the Spanish ambassador to appear at the Ministry of Foreign Affairs after a Spanish minister accused Maduro of running a “dictatorship”.

Venezuela was also angered by the decision of Spanish Prime Minister Pedro Sanchez to meet with Venezuelan opposition candidate Edmundo Gonzalez, who went into exile in Spain last week after being threatened with arrest by Maduro’s government.

Caracas has also had new tensions with Washington, which recognised Gonzalez as the winner of the July 28 election.

The US also imposed new sanctions on Venezuela earlier this week.