According to shipping data from the tracking website MarineTraffic, the ship, called Golsan, moored at Venezuela’s northern port of La Guaira on Monday night, Reuters reported.
It had left Shahid Rajaei port in southern Iran more than a month ago and sailed through the Suez Canal.
The Golsan approached Caribbean waters Friday following a high-seas journey from Iran.
The US seeks to oust Venezuelan President Nicolas Maduro, backing his political rival Juan Guaidó.
Maduro blames many of the problems on US sanctions and other measures to undermine his rule. He says the US wants to install a puppet government so it can exploit Venezuela's vast resources.
Former US National Security Adviser John Bolton writes in his book that President Donald Trump had insisted on military options against the South American nation, because “it’s really part of the United States.”
However, Maduro remains in power, and deep gasoline shortages that recently hit the capital of Caracas have eased since the Iranian tankers delivered fuel.
With Iran's recent technical help, Venezuela has also managed to get the Paraguana Refinery Complex, one of the largest in the world, partially working and producing gasoline.