Venezuelan intelligence officials arrested a high-ranking employee of opposition leader Juan Guaidó following a raid on his home in Caracas, says the legislature.
Mr Guaidó has called for the immediate release of his Chief of Staff Roberto Marrero, whose whereabouts are unknown.
The nearby house of the opposition legislator Sergio Vergara was also invaded. He was not arrested.
The operation could signal an attack on the opposition by embattled President Nicolás Maduro.
Mr Guaidó, chairman of the opposition-controlled National Assembly, declared himself an interim leader on 23 January ̵
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On Twitter he said Mr Marrero had been "kidnapped" "Two rifles and a grenade had been planted in his aide's house during the raid at around 02:00 local time (06:00 GMT)
Mr. Vergara, who lives in the same building, said more than 40 heavily armed officers of the Sebin Intelligence Service participated in the raids on the two homes. Mr Vergara added that his driver had also been arrested.
The Ministry of Information of Venezuela did not comment.
What is the background?
The raids occur at a time of high tensions in the country, along with Mr Guaidó and Mr Maduro Everyone claimed to be the constitutional president of Venezuela.
Soon after Mr. Guaidó was appointed Interim Chief, his assets were frozen and the Supreme Court, which was dominated by government loyalists, imposed a travel ban on him.
But the 35-year-old opposition leader opposed this ban last month, when he was touring in Latin American countries to gain support, and was generally expected to be arrested on his return.
Mr Guaidó continued to urge President Maduro to resign and called on the security forces, who were mainly loyal to the government.
Last week, the chief prosecutor said he had asked the Supreme Court to investigate Mr. Guaidó for allegedly sabotaging the country's electrical system following the power outage of the month.
Mr. Guaidó has been recognized as leader by more than 50 countries, most of them in Latin America and the USA. Mr. Maduro, who still has the support of China and Russia, accuses the opposition of being part of a US-orchestrated coup.