CARACAS, Venezuela — The top United States diplomat in Venezuela urged the authorities there on Friday to ensure transparency in the case of a jailed American whose trial has become another sore spot in relations between the two nations.

The diplomat, Todd D. Robinson, said that he reminded Foreign Minister Jorge Arreaza in a recent meeting of his “responsibility to guarantee transparency” in the case of the detained American, Joshua Holt.

Mr. Robinson also pressed for United States consular access to Mr. Holt, a 25-year-old Utah man whose mother recently voiced concerns about his health. The head of the United States Embassy in Venezuela before Mr. Robinson’s arrival had been denied access to a hearing in December.

“Without the ability to talk with him it’s difficult to know exactly what is happening,” Mr. Robinson said.