It did not give a reason for the move, but US Vice-President Mike Pence said Beijing had refused to grant a visa to the Venezuelan representative designated by opposition leader Juan Guaido. "We have already identified some", he said on state television, showing screenshots from Marrero's phone as proof and accusing the U.S. of running the operation.
He showed screen grabs of cell phone conversations that he said are proof Marrero was orchestrating the hitmen's payment.
President Nicolas Maduro has refrained from having Guaido arrested, but analysts say Marrero's detention was a clear attempt to weaken his political foe.
Guaido characterized the operation as a sign that Maduro is losing his grip on power.
Workers from Venezuela's state oil company, PDVSA, participate in an "anti-imperialist" march to support Venezuelan President Nicolas Maduro, in front of the Miraflores Presidential Palace in Caracas, Venezuela, January 31, 2019.
"We would like to inform the national and worldwide communities that our intelligence services have dismantled ... a terrorist cell that was planning to carry out a series of targeted attacks", Reverol said in a broadcast on state channel Venezolana de Television.
As he was taken away Mr Marrero, a lawyer who has been an activist against the leftwing governments of Venezuela for more than a decade, shouted to neighbours that police...
"The regime's continued use of kidnapping, torture, and murder of Venezuelan citizens will not be tolerated by the USA or the worldwide coalition that is united behind President Guaido".
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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 U.S.is urging countries within the Western Hemisphere to denounce Venezuelan President Nicolas Maduro and support Juan Guaido, leader of the National Assembly who's been recognized as interim president by more than 50 nations.
Marrero recorded a voice message as SEBIN agents were trying to enter his home in Caracas' upscale Las Mercedes neighborhood, which Guaido's press team forwarded to reporters.
Writing in the Miami Herald, the United States vice-president, Mike Pence, said Marrero's "kidnapping" was "the most recent example of Maduro's brutality and despotism".
China, which is seeking to make inroads into what has traditionally been regarded as the United States' backyard, disagrees and remains one of Maduro's main allies.
"This illegal coercive measure will affect 23,950,280 clients (individuals, as well as state and private companies) in Venezuela", the foreign ministry said. The government will replace electrical appliances damaged by the outages, widely seen as resulting from mismanagement and an exodus of qualified personnel but which he blamed on a USA conspiracy to oust him.
The State Department said on the same day that "the USA government today determined that persons operating in Venezuela's financial sector could be subject to sanctions".
"Do not test the resolve of this Administration", US National Security Advisor John Bolton tweeted.