The network also benefits the regime of Syrian President Bashar al-Assad, the US Treasury Department said in a news release.
The move is the latest by the US to pressure Iran since Washington withdrew from an international nuclear deal designed to prevent Iran from developing nuclear weapons.
After it withdrew, the US reinstated crippling economic sanctions on Tehran, including a ban on oil exports. In response, Tehran has carried out its plan to gradually stop implementing the nuclear deal.
The Treasury Department said the newly sanctioned shipping network's actions are part of a series of provocations that destabilize the region and the world.
"Treasury's action against this sprawling petroleum network makes it explicitly clear that those purchasing Iranian oil are directly supporting Iran's militant and terrorist arm, the IRGC-Qods Force," said Treasury Secretary Steven Mnuchin.
Treasury referred to it as a "vast oil-for-terror shipping network" and named 16 entities and 10 individuals in its sanctions announcement.
The US also announced a reward of up to 15 million dollars for information leading to the disruption of the financial networks run by the IRGC and its branches, including illicit oil sales.
Brian Hook, the US special representative for Iran, said the US would continue intensifying its maximum pressure campaign on Iran.
"There will be more sanctions coming," he told reporters at the State Department, adding that the US will continue to deny the Iranian regime revenue.
"We believe this creates the atmosphere that will eventually lead to talks," he said.
US President Donald Trump told reporters at the White House that Iran wants to come to the negotiating table.
Asked whether the new sanctions were a precursor to talks, he said the US would wait to see what happens.
"They want to talk. They want to make a deal. Iran is not the same country they were two and a half years ago," Trump said. "Iran is a country with tremendous potential. We’re not looking for regime change."
The sanctions announced Wednesday come one day after US sanctioned Iran's space agency for the first time. Last week the US slapped sanctions on an Iranian oil tanker and its captain at the centre of a diplomatic dispute, claiming that Iran still plans to send the ship to Syria.
The Treasury Department also issued a new advisory to warn the maritime community of the risks involved with participating in illicit schemes such as the IRGC-QF's alleged shipping network. The advisory is in addition to an earlier one warning of the risk of sanctions related to oil shipments to Syria, including those from Iran.
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