Iran has released the crude oil belonging to Turkish refiner Tüpraş that was carried by a Greek-owned, Marshall-Islands-flagged tanker Tehran seized in the Gulf of Oman earlier this year, a shipping source said on Thursday.

The vessel, M/T St. Nikolas, is still being held by Iran, the source told Reuters. It was laden with 1 million barrels of Iraqi crude oil destined for Türkiye when it was seized.

"The cargo was released earlier this week after negotiations," the source said.

Tüpraş said in a statement that St. Nikolas had been holding around 1 million barrels of crude oil that it had purchased from the Iraqi state oil company SOMO.

"The entire cargo was recovered through a ship-to-ship transfer conducted between July 23-25, 2024. The crude oil is now en route to the refinery and is expected to arrive in September," Tüpraş said.

The cargo was transferred onto the Türkiye-flagged tanker T. Semahat earlier this week via a ship-to-ship transfer near Iran's Larak Island, said Claire Jungman, chief of staff at U.S. advocacy group United Against Nuclear Iran, which tracks Iran-related tanker traffic via satellite data.

T.Semahat's Türkiye-based operator Ditas is majority-owned by Tüpraş.

The vessel had the port of Fujairah in the United Arab Emirates (UAE) as its destination and was sailing away from Iran on Thursday, LSEG shipping data showed.

Iran seized the St. Nikolas in January in retaliation for the confiscation last year of the same vessel and its oil by the U.S., Iranian state media had reported at the time.