A judge in Venezuela has ordered a trial in the case of six American oil executives held for 18 months on corruption charges that have contributed to tensions with the U.S.

During a hearing Friday, judge Rosvelin Gil dismissed a defense request that the six employees of Houston-based Citgo be released from prison and the charges against them dropped. Fifteen previous hearings had been canceled.

The executives, five of whom are American citizens, flew on a corporate jet to Caracas in 2017 to attend a board meeting. Once there they were arrested by masked security agents.

President Nicolás Maduro's government later accused them of embezzlement stemming from a proposal to refinance billions in Citgo bonds by offering up a 50 percent stake in the company as collateral.