As three Iranian tankers make their way around the Cape of Good Hope en route to Venezuela, another vessel from Iran has reportedly turned up in South America.

Oil intelligence outfit TankerTrackers tweeted over the weekend that an Iranian VLCC carrying gas condensate had turned up at Jose Terminal in Venezuela.

"Most likely sailed all the way around southern Africa given her [automatic identification system (AIS)] transponder was switched off," one of the tweets read.

"Name & IMO number has been painted over. Goes by new name: HONEY."

TankerTrackers said the gas condensate would probably be used to help Venezuela blend its crude oil, increasing output from its refineries.

Iran is also said to be sending three product tankers — the 35,200-dwt National Iranian Tanker Co trio Forest, Fortune and Faxon (all built 2004) — to Venezuela along the same route.

Maritime security consultancy Dryad Global said the move is a test by Iran to see how the US would react, while sending a message that its oil exports will not be interrupted.

The US has long sought to topple the regimes in Tehran and Caracas, and its aggressive sanctions campaign has pushed the two countries closer together.

In late May and early June, five Iran-flag, gasoline-laden tankers arrived in Venezuela.

Tehran attempted another shipment in July using four Greek-owned tankers, but in August, US officials said they had persuaded the ships' owners to offload the cargo after securing a court order seizing it.

Of the trio currently under way, the most recent AIS broadcast came from the Faxon on Sunday, which showed it southeast of Durban. The Forest and Fortune last broadcast on Saturday.

There are 179 ships with links to Iran and Venezuela already sanctioned by the US that are able to carry out trade between the two countries, including 65 oil tankers.

Washington has limited options to stop shipments between the two countries. The most direct would be military intervention, which would come with a steep diplomatic cost.