A picture taken on July 21, 2019, shows Iranian Revolutionary Guards patrolling around the British-flagged tanker Stena Impero as it's anchored off the Iranian port city of Bandar Abbas.

DUBAI — Iran has seized a foreign tanker in the Gulf carrying 700,000 liters of fuel, Iranian state TV said Sunday, citing the country's Revolutionary Guards.

Seven sailors on board have also been detained, according to Revolutionary Guard commander Ramezan Zirahi, who was quoted by Al Mayadeen TV.

"The IRGC's naval forces have seized a foreign oil tanker in the Persian Gulf that was smuggling fuel for some Arab countries," state TV quoted Zirahi as saying.

"It carried 700,000 liters of fuel. Seven sailors onboard of the tanker, who are from different nationalities, were detained." The tanker's origin is unclear. The U.S. Navy's Fifth Fleet in Bahrain said it did not have sufficient information to confirm the reports.

On July 19, Iranian commandos seized a British-flagged tanker, the Stena Impero, in the Strait of Hormuz on grounds of alleged maritime violations. The U.K. government has called the seizure illegal. The incident followed British forces capturing an Iranian tanker near Gibraltar, which it accused of violating sanctions on Syria.

Last week a second British warship arrived in the Strait of Hormuz, the narrow waterway for 30% of the world's seaborne oil, to protect British tankers. U.K. Foreign Secretary Dominic Raab has urged Iran to "come out of the dark" and release the Stena Impero.