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Venezuelan President Nicolas Maduro welcomed a visit by a top-ranking Republican congressional staffer last month to discuss the possible release of a Utah man jailed for more than 20 months in this volatile South American nation, six U.S. congressional and administration aides told The Associated Press.

It's not known if there has been any progress in the backchannel talks to secure Joshua Holt's freedom, but the mere fact that Maduro met with the staffer, and in turn sent an envoy of his own this week to Washington, may be a sign of movement in a case that has become a major irritant as tensions between the two countries rise.

The unannounced discussions began when Caleb McCarry, a Republican aide on the Senate Foreign Relations Committee, traveled to Caracas in February and met with Maduro and first lady Cilia Flores to discuss Holt's imprisonment, said the aides, who agreed to discuss the matter only if not quoted by name because the talks are sensitive.

They said McCarry, who has known Maduro for more than 15 years, made the unusual visit at the request of Sen. Orrin Hatch, a Republican from Utah. While in Caracas, McCarry visited Holt in jail, delivering him a letter from Hatch.

The Trump administration is said to be aware of McCarry's lobbying, though there is no indication it has lent support to the effort. State Department spokeswoman Heather Nauert declined to comment Monday when asked about the informal talks, saying only: "We are disappointed Mr. Holt has still not been released on humanitarian grounds."

The behind-the-scenes dialogue prompted a surprise visit this week to Washington by a trusted ally of Maduro, Gov. Rafael Lacava of Carabobo state, to discuss Holt, three congressional aides familiar with the visit said.

Holt, 25, traveled to Caracas in June 2016 to marry a fellow Mormon he met online practicing his Spanish. The couple was waiting for her U.S. visa when they were arrested during a police raid on the government-built housing complex where they were living in her apartment. Venezuelan authorities alleged Holt was stockpiling "weapons of war."

U.S. officials have repeatedly demanded Holt's release on humanitarian grounds, considering the charges against him and his wife, Thamara Candelo, to be trumped up and politically motivated.

His imprisonment while awaiting trial in a Caracas jail where some of Maduro's chief opponents are being held has further strained relations already marred by U.S. sanctions and almost-daily accusations by Maduro that the U.S. is working with his opponents to topple his socialist administration. Secretary of State Rex Tillerson on a recent trip to South America warned that the U.S. may slap crippling oil sanctions on Venezuela and cheered on the prospect of the Venezuelan military overthrowing Maduro.

The visit by Lacava, who traveled to Washington on Sunday after being granted a U.S. visa, has been met with hostility by Sen. Marco Rubio, a Florida Republican who is a harsh critic of Maduro and has President Donald Trump's ear on policy toward Venezuela.

Rubio, in an email sent by his office to fellow Republicans on the Foreign Relations Committee, decried Lacava's visit as an attempt to negotiate Holt's freedom in exchange for sanctions relief or the release of the first lady's two nephews who were convicted last year in a New York federal court for drug trafficking.

The message cites press reports about Lacava's alleged involvement in money laundering and other criminal activity. It also says Rubio has received assurances from the White House and State Department that no one in the Trump administration will meet with Lacava.

"The fact that Rafael Lacava is even coming to the U.S. to negotiate a sanctions-for-hostage deal proves that Holt is being held as leverage," says the email, a copy of which was obtained by AP and whose authenticity was confirmed by Rubio's office. "The very news of high-level meetings would be used by Maduro to sow confusion and doubt in the minds of our regional allies about the commitment of the United States to sanctions."

Lacava could not be reached and has not commented publicly since Rubio criticized him in a tweet Sunday. Venezuela's Communications Ministry declined to comment.

One congressional aide said that Lacava had only requested meetings on Capitol Hill and that the sole purpose of those meetings is to urge the release of Holt and not negotiate anything in exchange. Any discussion of sanctions relief that may be on Lacava's agenda is unlikely to come up, since that is a matter for the administration to decide, the aide added.

McCarry knows Maduro from their time together on the Boston Group, an informal gathering from across the political spectrum — Democrats, Republicans, socialists and capitalists — from both countries that worked discreetly to repair relations between the two countries following a brief coup in 2002 against then-President Hugo Chavez. The U.S. recognized the government that arose briefly from the failed coup.

Maduro and Flores were members of the Venezuelan delegation of lawmakers that traveled to Massachusetts, along with U.S. representatives like then-Sen. John Kerry. McCarry at the time worked for one of the Republican founders of the now-defunct group and over the years has maintained ties to many Venezuelan officials. He also accompanied Sen. Bob Corker, a Tennessee Republican who is chairman of the Foreign Relations Committee, on a trip to Caracas in 2015.

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Joshua Goodman on Twitter: https://twitter.com/APjoshgoodman