The vessel was intercepted near Iran's Farsi Island in the Gulf, Iran's semi-official Fars news agency said. Lebanon's al-Mayadeen TV station reported that it was seized on Wednesday.
"The IRGC's naval forces have seized a foreign oil tanker in the Persian Gulf that was smuggling fuel for some Arab countries," state television quoted Islamic Revolutionary Guard Corps (IRGC) commander Ramezan Zirahi as saying.
It was carrying 700,000 liters of fuel, he said. Seven crewmen of different nationalities were detained.
"The seizure of the oil tanker was in coordination with Iran's judiciary authorities and based on their order," Fars quoted him as he as saying.
Tensions have risen between Iran and the West since last year when the United States pulled out of an international agreement which curbed the Tehran's nuclear program in return for an easing of economic sanctions on Iran.
In July, British forces seized an Iranian oil tanker near Gibraltar, accused it of violating sanctions on Syria.
Then Iran seized a British tanker in the Strait of Hormuz for alleged marine violations. It allowed a second one to proceed after issuing a warning.
Describing the seizure of the Stena Impero in the Strait of Hormuz as illegal, Britain has rejected the idea that it could release the Iranian tanker in exchange for the British-flagged vessel seized by the Revolutionary Guards.
