Pompeo said in a tweet on his Twitter account that he attached a satellite image showing the oil tanker Adrian Daria I near the Syrian coast.
"Will the world hold Iran accountable if this oil is delivered to Syria?" Pompeo added.
Pompeo had previously accused Zarif of lying, saying in an interview with CBS News's "Face the Nation" program. "I don't know why anyone listens to the Iranian foreign minister? Zarif has nothing to do with Iranian foreign policy. He lied for decades and then resigned."
The Iranian news agency quoted a spokesman for the Foreign Ministry that the Iranian tanker, the focus of the dispute between Tehran and the West, delivered its cargo after stopping on the Mediterranean coast.
The agency quoted Abbas Moussavi: "Iranian oil tanker Adrian Daria 1 stopped eventually at the shores of the Mediterranean ... and unloaded."
The tanker "Adrian Daria 1" has closed the transmitters and receivers off the Syrian coast early last month and took satellite images of it off the Syrian port of Tartous.