Juan Guaido, the opposition leader backed by the US and other countries as Venezuela's interim leader, has said he, as well as his close circle, "won't be intimidated" following the arrest of his chief of staff by President Nicolas Maduro's regime.
The arrest of Roberto Marrero, Mr Guaido's aide, in a predawn raid was a "vile, vulgar kidnapping," he told at a news conference, but "it won't make us deviate from the path we are on."
According to Juan Guaido and other members of the opposition, around 15 intelligence officers grabbed Mr Marrero and took him to an unknown location.
An opposition lawmaker, who lives in the same building, told journalists his home was also raided but he was not arrested.
The US has warned Nicolas Maduro's government against touching the opposition leader or his inner circle, threatening unspecified consequences.
US President Donald Trump has said repeatedly he was considering "all options" in his drive to remove President Maduro from power and see Juan Guaido take charge.
The situation in Venezuela is at an impasse, however, with President Maduro daily denouncing a US "imperialist" plot to dislodge him, and Mr Guaido rallying supporters in a nationwide tour.
US Secretary of State Mike Pompeo demanded via Twitter Roberto Marrero's "immediate release," warning that the US government will hold accountable those involved.
