CARACAS (Reuters) - Venezuelan authorities detained opposition leader Juan Guaido’s chief of staff on Thursday in a pre-dawn raid, an escalating crackdown by President Nicolas Maduro against his opponents that the White House said would “not go unanswered.”

Maduro’s government accused Roberto Marrero of planning attacks against top political figures, which the opposition said was false and an act of intimidation.

U.S. President Donald Trump’s national security adviser, John Bolton, called for the immediate release of Marrero and warned that “Maduro has made another big mistake,” adding that the arrest “will not go unanswered.”

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 called for 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.

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

A U.S. State Department spokesman condemned the raids as a sign that “Maduro is betting on repression to hold on to power. It will not stand. There will be consequences for a continued crackdown.”

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.”

While Trump has said all options remain open, there appears to be little support in Washington or regional Latin American capitals for any military intervention.

INTELLIGENCE SERVICE RAIDS

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 the opposition would not work.

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“As they cannot take the interim president prisoner, so they seek out people closest to him, threaten relatives, carry out kidnappings,” Guaido told a news conference.

U.S. State Department officials believe they know who was responsible and will take steps to hold those people accountable, Secretary of State Mike Pompeo said in an interview with Fox News later on Thursday.

Venezuelan Interior Minister Nestor Reverol said authorities had seized an arms cache from Marrero during the raid and said he was “directly responsible for the organization” of criminal groups. On state television, Reverol showed an image of two rifles that Marrero allegedly had in his possession.

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Guaido had said earlier that SEBIN agents had planted two guns and a grenade in Marrero’s home during the raid. Rights groups say Venezuelan authorities have a long history of planting evidence to justify charges against opposition politicians and activists, which the government denies doing.

SEBIN agents also arrested Vergara’s driver, Luis Aguilar, who Reverol later accused of being Marrero’s bodyguard.

Maduro said in a televised broadcast that authorities were in the process of “dismembering the whole terrorist group and turning them over to the justice system,” without mentioning Marrero or Guaido.

The United Nations human rights office tweeted its concern and urged the government to respect due process. The Lima Group regional bloc also denounced Marrero’s arrest and said Maduro was responsible for his safety.

Since January, Venezuelan authorities have arrested over 1,000 people in connection with anti-government demonstrations, most of them arbitrarily, rights groups say. Guaido himself was briefly detained by intelligence agents in January.

UN human rights chief Michelle Bachelet, who has sent a mission to Venezuela to assess the situation, said on Wednesday that Maduro’s security forces, backed by pro-government militias, had quashed peaceful protests with an excessive use of force, killings and torture.

Maduro has said his government is the victim of an “economic war” led by his political adversaries and blames U.S. financial and oil sector sanctions for the country’s situation.

Venezuela is reeling from annual inflation topping 2 million percent, which has fueled malnutrition and preventable disease and spurred an exodus of more than 3 million citizens since 2015.