Venezuelan opposition leader and self-declared interim president Juan Guaido says intelligence agents working for President Nicolas Maduro have arrested his chief of staff.
Guaido aide Roberto Marrero was taken into custody in an overnight raid on his home.
"We do not know his whereabouts," Guaido tweeted Thursday. "He must be released immediately."
Opposition lawmaker Sergio Vergara says agents also raided his own home. He is accusing the agents of planting weapons on Marrero.
U.S. Secretary of State Mike Pompeo is demanding Marrero's immediate release and said those behind the arrest will be held accountable.
National Security Adviser John Bolton tweeted, "Maduro has made another big mistake" that "will not go unanswered."
Detained oil executives
Also in Washington, Texas Republican senators John Cornyn and Ted Cruz said the Maduro regime must free six Citgo oil company executives who have been in jail since November 2017 for alleged money laundering and embezzlement.
Five of the executives are Texans.
"We are gravely concerned for their health and safety as they continue to be used as political pawns by an illegitimate government," the senators said Thursday. "Every day that passes for these families without their loved ones is excruciating."
Cornyn and Cruz say the six are being held in deteriorating conditions and say Venezuelan authorities have denied them a trial and contact with the State Department.
Citgo is a U.S.-based refinery and gasoline marketer primarily owned by Venezuela's state-run oil company, PDVSA.
Because of U.S. sanctions on PDVSA, Citgo's profits are being placed in a blocked account so the Maduro government cannot access it.
Maduro and Guaido are battling for control of Citgo, the main source of cash from the United States.
Support for Guaido
The United States and about 50 other countries recognize Guaido as Venezuela's legitimate president and say Maduro must go.
President Donald Trump has said all options are on the table for Venezuela, but has neglected to say under what circumstances he would use U.S. military force.
A collapse in world energy prices, corruption and failed socialist policies have destroyed oil-rich Venezuela's economy.
Food and medicine are scarce, and more than 3 million Venezuelans have fled the country.
Maduro has shown little tolerance for dissent. He has blamed his country's problems on the United States, and accuses the U.S. of backing the opposition in plotting a coup.
Wayne Lee contributed to this report.