A senior U.S. diplomat quietly traveled to Venezuela this week and met with imprisoned Americans in an ongoing effort to secure release of the men the Biden administration believes are being held as bargaining chips by a top U.S. adversary, The Associated Press has learned.

Roger Carstens, the special presidential envoy for hostage affairs and the government’s top hostage negotiator, arrived in Caracas on a chartered flight Tuesday evening and returned home Friday in a previously unreported visit.

It was the first known face-to-face outreach by a top U.S. official since the Trump administration shuttered the American Embassy in Caracas in March 2019 after recognizing opposition leader Juan Guaidó as Venezuela’s legitimate leader. Ever since, relations between the two countries have grown steadily more hostile, with the U.S. government imposing strict oil sanctions on the country and targeting top officials with criminal indictments, something President Nicolás Maduro has likened to a “soft coup.”