Guaido invoked the constitution in January to assume the interim presidency after declaring Maduro’s 2018 re-election a fraud. He has been recognized by the United States and dozens of other Western nations as the country’s legitimate leader.

Maduro, who has overseen a dramatic collapse of the OPEC nation’s economy, has called Guaido a puppet of the United States and said he should “face justice,” but has not explicitly ordered his arrest.

Top U.S. officials have repeatedly warned Maduro not to touch Guaido and his inner circle, but it is unclear what more they can do.

They have threatened ever harsher sanctions intended to further isolate Maduro and cut off his administration’s sources of revenue, but the humanitarian and political costs of further blanket measures could be high. Millions of Venezuelans are already suffering shortages of food and medicine.

U.S. President Donald Trump’s national security adviser, John Bolton, called for the immediate release of Roberto Marrero.

“Maduro has made another big mistake,” Bolton said on Twitter, adding that the arrest “will not go unanswered.”

“The toughest sanctions are yet to come,” he said. “Unless Maduro’s usurpation ends, he and his cronies will be strangled financially.”

The United States imposed sanctions on Venezuela’s state-owned oil company PDVSA in January, preventing U.S. companies from dealing with it unless revenues went to a fund available to Guaido, but has not yet slapped sanctions on companies from other countries that do business with PDVSA, a practice known as “secondary sanctions.”

Guaido said the raids by agents from the SEBIN intelligence service on the residences of Marrero and another opposition legislator, Sergio Vergara, showed Maduro’s “weakness” and that attempts to intimidate him would not derail the opposition campaign.