UPDATE 5-Venezuela detains top aide to Guaido in test of Washington's support

Venezuelan opposition leader Juan Guaido said on Thursday intelligence agents had detained his chief of staff during a pre-dawn raid, putting to the test repeated U.S. warnings that President Nicolas Maduro should not go after his opponents. U.S. Secretary of State Mike Pompeo called on Twitter for Roberto Marrero's immediate release and said "we will hold accountable those involved."

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 and threatened ever harsher sanctions intended to further isolate Maduro and cut off his administration's sources of revenue. U.S. National Security Adviser John Bolton warned Maduro this month that Guaido's safety must be guaranteed and that the world was watching. 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.

"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. 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.

"I am in my house and the SEBIN is here. Unfortunately, they have come for me. Keep up the fight, don't stop and look after (Guaido)," Marrero said. Vergara, Marrero's neighbor, said some 40 armed SEBIN agents forced their way into their homes and spent three hours inside. The SEBIN left with Marrero and Vergara's driver, the legislator said in a video posted on his Twitter account.

Guaido said that Marrero had told Vergara that agents had planted two rifles and a grenade in his house. Venezuela's Information Ministry did not immediately respond to a request for comment.

"HELD TO ACCOUNT" Since January, Venezuelan authorities have arrested over 1,000 people in connection with anti-government demonstrations, most of them arbitrarily, rights groups say.

United Nations human rights chief Michelle Bachelet said on Wednesday that Venezuelan security forces, backed by pro-government militias, have quashed peaceful protests with an excessive use of force, killings and torture. On Thursday, the UN human rights office tweeted its concern over Marrero's detention and urged the government to respect due process and reveal his whereabouts.

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. With Washington already having imposed extensive sanctions on Caracas, the humanitarian and political costs of further blanket measures could be high, with millions of Venezuelans already suffering shortages of food and medicine.

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

Guaido traveled around South America in February to drum up diplomatic support for his government, defying a travel ban imposed by the pro-government Supreme Court. He later entered the country via Venezuela's principal airport without being detained by immigration officials.

Venezuela's chief state prosecutor, Tarek Saab, last week asked the Supreme Court to open an investigation into Guaido for alleged involvement in the "sabotage" of the country's electrical network, after the longest nationwide power blackout in decades. The opposition, along with electrical experts, said the power outage was due to the government's incompetence and years without maintenance.

(Reporting by Brian Ellsworth and Vivian Sequera; Additional reporting by Corina Pons; Writing by Angus Berwick Editing by Daniel Flynn, Bernadette Baum and Rosalba O'Brien)