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(Reuters) - U.S. Republican Senators Ted Cruz and John Cornyn on Thursday pressed Venezuelan President Nicolas Maduro to release six executives from Houston-based oil company Citgo Petroleum that have been in jail in the country since 2017.

The former top employees of Venezuelan PDVSA’s refining subsidiary, most of whom are U.S. citizens, were arrested in late 2017 and accused of embezzlement and money laundering linked to talks to refinance Citgo’s debt.

Family members of Jose Luis Zambrano, Alirio Zambrano, Jorge Toledo, Tomeu Vadell, Gustavo Cardenas and Jose Pereira have asked the U.S. government to intervene, citing health concerns for the men.

Venezuela has denied them contact with U.S. State Department representatives, the two senators said.

“We are gravely concerned for their health and safety as they continue to be used as political pawns by an illegitimate government. We call for their immediate release,” the senators said in a release.

The Venezuelan government is battling over Citgo with a group led by Venezuela’s opposition leader Juan Guaido, which has appointed its own board to run Citgo.

Elliott Abrams, the U.S. special representative for Venezuela, earlier this month told senators the Trump administration has been unable to get consular access to the six executives despite court orders issued for their release.

“We will continue to work with the administration to ensure these aggressive actions by the Maduro regime are met with the appropriate action,” the senators said.