Venezuela's Supreme Court has ordered a top deputy of opposition leader Juan Guaido to be held in preventive detention at a military prison in Caracas.
Edgar Zambrano, the deputy speaker of the opposition-majority National Assembly, was jailed for "the flagrant commission of the crimes of treason, conspiracy and civil rebellion," the court said.
Mr Zambrano had been arrested by President Nicolas Maduro's intelligence service on Wednesday for supporting a failed 30 April uprising organised by Juan Guaido.
The 64-year-old's car had been surrounded outside his Democratic Action Party's headquarters before it was towed, with him still in it, to the notorious Helicoide prison.
He narrated the drama in real time on Twitter, while images of the incident also circulated on social media.
"Democrats, keep up the fight!" tweeted Zambrano.
Edgar Zambrano is deputy to National Assembly speaker Guaido, who organised the revolt by around 30 members of the armed forces, many of whom subsequently fled to the Brazilian embassy.
Venezuela was plunged into turmoil in January when Juan Guaido declared himself acting president in a direct challenge to Nicolas Maduro's authority.
He has since been recognised as interim president by more than 50 countries as he steps up the pressure to oust president Maduro, whom he considers illegitimate after 2018 elections widely seen as fraudulent.
But the socialist leader remains steadfast, backed by Venezuela's powerful military high command.
"We warn the people of Venezuela and the international community: the regime has kidnapped the first vice-president" of the National Assembly, said Mr Guaido.
"They are trying to destroy the power representing all Venezuelans, but they will not achieve it," he added.
The United States, European Union and several Latin American states have criticised Mr Zambrano's arrest.
On the Twitter account of its now-closed embassy in Caracas, Washington called the detention "illegal and inexcusable," warning of "consequences" if he is not immediately released.
US President Donald Trump - whose government was among the first to back Juan Guaido - said he was "discussing the terrible abuses by Maduro."
President Trump did not mention Edgar Zambrano but said the US would stand with the people of Venezuela "for however long it takes."
The EU and several of Venezuela's neighbours protested Mr Zambrano's arrest while the country's Foreign Minister Jorge Arreaza vowed to bring to justice "accomplices to an unconstitutional military uprising".
Venezuela's Supreme Court meanwhile added three more lawmakers to the seven already indicted for treason and conspiracy over their backing of Juan Guaido's uprising.
Attorney General Tarek William Saab says the two days of clashes that followed left six people dead.
The Constituent Assembly, which Nicolas Maduro created to sideline the National Assembly, has said it would suspend the immunity of any lawmakers who backed the uprising.
Mr Guaido said in a speech after the first indictments on Tuesday that the government's "only response... is to persecute, because they no longer govern, because they no longer have command."
Venezuela has suffered five years of recession that has seen more than 2.7 million people flee poverty, hyperinflation, food shortages and insecurity since 2015, according to United Nations figures.