A South Korean delegation arrived in Iran on Thursday amid tensions following the seizure of a South Korean oil tanker and its crew by Iranian forces in sensitive Gulf waters this week.

Iran's Revolutionary Guards said Monday it had seized the South Korean-flagged Hankuk Chemi for infringing maritime environmental laws.

The Guards said the vessel was carrying 7,200 tonnes of "oil chemical products" and that the detained crew were from South Korea, Indonesia, Vietnam and Myanmar.

The South Korean delegation, led by the director-general of the foreign ministry's Middle Eastern affairs department, boarded a plane early Thursday and was set to arrive in Tehran via Doha.

The South Korean delegation led by Koh Kyung-sok (L) is heading to Iran to negotiate the release of an oil tanker and its crew seized in strategic Gulf waters
The South Korean delegation led by Koh Kyung-sok (L) is heading to Iran to negotiate the release of an oil tanker and its crew seized in strategic Gulf waters YONHAP / -

"I plan to meet my counterpart at the Iranian foreign ministry and will meet others through various routes if it will help efforts to resolve the issue of the ship's seizure," said Koh Kyung-sok, the chief delegate, before boarding the plane.

But the government spokesman in Tehran gave a different version of the reason for the visit.

In a statement late Thursday Said Khatibzadeh said it was an advance delegation ahead of a visit Sunday by South Korean deputy foreign minister Choi Jong-Kun.

The visit by the South Korean delegation "had been agreed before the seizure" of the Hankuk Chemi oil tanker, "and its main goal is to discuss ways of accessing Iranian funds in Korea", Khatibzadeh said.

Iran's seizure of the tanker came after Tehran had urged Seoul to release billions of dollars of Iranian assets frozen in South Korea under US sanctions.

The South Korean-flagged tanker Hankuk Chemi being escorted by Iranian navy boats after being seized in the Gulf
The South Korean-flagged tanker Hankuk Chemi being escorted by Iranian navy boats after being seized in the Gulf TASNIM NEWS / -

Iran was a key oil supplier to resource-poor South Korea until Washington's rules blocked the purchases.

Seoul has said that South Korea's deputy foreign minister would discuss the frozen assets during his three-day visit to Iran, and the trip would go ahead despite the seizure.

According to Iranian government spokesman Ali Rabiei, Iran has "$7 billion of deposits in South Korea".

The money can neither be transferred nor earn interest, yet Iran is charged fees on it, he has said.

The Hankuk Chemi incident was the first seizure of a major vessel by the Iranian navy in more than a year.

In July 2019, the Guards seized the British-flagged oil tanker Stena Impero in the sensitive Strait of Hormuz for allegedly ramming a fishing boat. They released it two months later.

At the time it was widely seen as a tit-for-tat move after authorities in the British overseas territory of Gibraltar detained an Iranian tanker and later released it over US objections.

Tehran denied the two cases were related.

The Guards seized at least six other ships in 2019 over alleged fuel smuggling.

South Korea