Revolutionary Guard Corps' seizure of MT Hankuk Chemi in Gulf waters comes at a time of tension between Tehran and Seoul over Iranian funds frozen in South Korean banks.
Iran has seized a South Korean-flagged oil tanker in the Strait of Hormuz over alleged "environmental hazards" and "oil pollution."
"A Korean ship was seized in Persian Gulf waters by the Revolutionary Guard's navy and transferred to our country's ports," Fars news agency and other local media reported on Monday.
"This tanker had a South Korea flag and was seized over oil pollution and environmental hazards."
Earlier a security firm said the vessel, MT Hankuk Chemi, which bound for the United Arab Emirates from Saudi Arabia, had gone into Iranian territorial waters.
It comes ahead of an expected visit by South Korea's deputy foreign minister to Tehran.
The Iranian Foreign Ministry said that the visit would happen in the coming days and would discuss Iran's demand that South Korea release $7 billion in funds frozen in South Korean banks because of US sanctions.
South Korea demanded the "early release" of the oil tanker, saying the chemical tanker was seized by Iranian authorities in the waters off Oman.
South Korean forces stationed in the Strait of Hormuz have been dispatched to the area, a Foreign Ministry statement said.
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Tasnim is already publishing photos of #Iran #IRGC's seizure of the South Korean-flagged tanker MT Hankuk Chemi. pic.twitter.com/p0M2FI9ImC— Jason Brodsky (@JasonMBrodsky) January 4, 2021
Satellite data from MarineTraffic.com showed the tanker off Bandar Abbas coast.
The United Kingdom Marine Trade Operations, an information exchange overseen by the British royal navy in the region, acknowledged an "interaction" between a merchant vessel and Iranian authorities.
As a result, the UKMTO said the merchant vessel made an "alteration of course" north into Iran's territorial waters.
Commander Rebecca Rebarich, a spokeswoman for the US Navy's 5th Fleet, said authorities there were aware and monitoring the situation.
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Crew held in port city
The crew of the vessel has been detained in Bandar Abbas, the semi-official news agency Tasnim, reported.
The crew members are from South Korea, Indonesia, Vietnam, and Myanmar, Tasnim said, without specifying the number of detained crew members or where they were being held.