Venezuelan President Nicolas Maduro’s government has been accused of “forced disappearance” of six American oil executives jailed in Venezuela after the men mysteriously failed to show up for the scheduled start of their trial on Wednesday.

Lawyers for the six executives from Houston-based Citgo waited at a Caracas courthouse for more than six hours for the men to be transferred from jail by police. They never showed up, according to Veronica Vadell, whose father, Tomeu Vadell, is among the missing businessmen.

“Why is there a delay? Where are the men?" Vadell wrote on social media of the “hostage case.”

It’s not clear why police never transferred the men from the Helicoide jail in Caracas where they are believed to be held. Maduro’s chief prosecutor Tarek William Saab told The Associated Press Wednesday the trial was set to begin that day.

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The six oilmen were awaiting trial on corruption charges from a plan which never came to fruition to refinance $4 billion in bonds for the Citgo, which is owned by the state-run oil giant PDVSA. They were going to offer a 50 percent stake in the company as collateral. Prosecutors accused the men of maneuvering to benefit from the potential deal.

The men had been lured to Venezuela to attend a meeting at Citgo’s parent, PDVSA. They were hauled away by masked security agents from a meeting in Caracas before Thanksgiving in 2017.

The oilmen had been under house arrest when they were rounded up without explanation and placed in jail two weeks ago. Since then, they’ve had no access to contact their families or lawyers.

That same day, opposition leader Juan Guaidó, who has the backing of the U.S. and 60 other nations, met with President Trump at the White House, leading some to believe the detention might be politically motivated.

The initial judge postponed a preliminary hearing for the men, five naturalized U.S. citizens and one legal resident, 15 straight times, adding to speculation the men were being used as political pawns as relationships between the U.S. and Venezuela soured.

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Vice President Mike Pence met with family members of the detained at the White House in April. “We are going to stand with you until they are free and until Venezuela is free,” he said at the time.

The group includes Vadell, vice president of refining; Gustavo Cardenas, head of strategic shareholder relations as well as government and public affairs; Jorge Toledo, vice president of supply and marketing; Alirio Zambrano, vice president and general manager of Citgo’s Corpus Christi refinery; Jose Luis Zambrano, vice president of shared services; and Jose Angel Pereira, the president of Citgo.

The disappearance came one day after the Trump administration, in its most recent effort to stifle the cash flow to Maduro’s regime, announced new sanctions against a Russian state-controlled brokerage which the U.S. says helps the Venezuelan government skirt an American oil embargo.

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Last week, Guaidó defied a national travel ban to visit world leaders in Colombia, Europe, Canada and the U.S. After Guaido met with Trump in the Oval Office, he recognized him as the “legitimate president of Venezuela” during his State of the Union address. Guaidó had attended as the president’s guest.

The Associated Press contributed to this report.