Iran's OPEC governor, Hossein Kazempur Ardebili, is in a coma after suffering a "severe" brain hemorrhage.
In a tweet on May 3, the country's Oil Ministry said Ardebili was hospitalized on May 1. It did not provide further details.
Ardebili is a key figure in Iran's energy industry and served as the deputy foreign minister and deputy oil minister in the 1980s.
He was ambassador to Japan in the early 1990s, while at the same time serving as OPEC governor.
Iran has the world's fourth-biggest oil reserves and second-largest natural-gas reserves.
But its economy has been battered by sanctions imposed by the United States since U.S. President Donald Trump pulled Washington out of the Iran nuclear deal in 2018.
Washington's imposition of a full line of sanctions in November 2018 targeted key Iranian economic spheres -- including the banking and oil sectors -- and denied the government its main source of revenue while making international trade increasingly difficult.