(Reuters) - Six executives from U.S. refiner Citgo Petroleum held in a Venezuelan jail without a court hearing for more than a year have asked the U.S. State Department and lawmakers to help win their release, family members and lawyers said.

FILE PHOTO: Citgo Corpus Christi Refinery is seen in Corpus Christi, Texas, U.S., January 26, 2019. REUTERS/Erwin Seba/File Photo

Jose Luis Zambrano, Alirio Zambrano, Jorge Toledo, Tomeu Vadell and Gustavo Cardenas, all former vice presidents of the Houston-based company and most of them U.S. citizens, along with former Citgo President Jose Pereira were arrested in November 2017 after being called into a meeting at the Caracas office of parent company Petróleos de Venezuela, S.A., known as PDVSA.

The executives were accused of embezzlement, being public servants acting in concert with a contractor, money laundering and conspiracy in connection with a never-concluded agreement to refinance Citgo debt. A preliminary court hearing has not yet been held.

“They have robbed them of due process and their right to a timely trial,” a group of 13 family members and lawyers said in an open letter to the U.S. government seen by Reuters. “Top U.S. government intervention may be our only chance at releasing the six detainees.”

The attorneys did not want to be identified for fear of retaliation.

They said they contacted the U.S. State Department, several senators and congressmen before resorting to the media. The U.S. government has not provided any clear indication of progress on the cases, they said.

A State Department spokeswoman said on Friday it was unable to comment on the status of private U.S. citizens.

“We continue to work closely with international partners to ensure the safety and security of U.S. citizens in Venezuela,” she said in an email.

The plea emerged as a battle over Citgo’s fate by Socialist Nicolas Maduro’s government and a group led by the congress head Juan Guaido was sparked by U.S. support for the opposition. Guaido has said he wants to appoint a new board for the company, now in the hands of officials nominated by Maduro.

Attorneys for the executives have documents that show debt refinancing negotiations were approved by the PDVSA board. One document viewed by Reuters indicates the board in June 2017 approved the start of negotiations with Apollo Global Management LLC and its unit Frontier Management Group.

The deal was never signed. U.S. sanctions imposed in August 2017 scuttled any deal.

Apollo and Venezuela’s Attorney General office did not respond to requests for comment.

Maduro in 2017 began a corruption crackdown at PDVSA that led to dozens of executives being jailed, including former Citgo and PDVSA President Nelson Martinez. Martinez died in custody in December.

Executives “have been forced to sleep with the lights on and experience severe heat, lack of air circulation, constant and untreated sickness, overcrowding, malnutrition, and seeing less than 30 minutes of sunlight per month,” their families wrote.

“One of the reasons why I retired from Citgo was Vadell’s detention,” said Charles Alexander, a former Citgo manager whose contact information was provided by the executives’ families. “He has been inappropriately arrested and abused.”