Armed troops from Iran's Revolutionary Guard seized the ship Monday near the Strait of Hormuz in the Persian Gulf. The tanker was carrying 20 crew members.
The seizure appears to be an attempt to pressure South Korea to release around $7 billion frozen under American economic sanctions.
Critics of Iran have long accused the country of hijacking ships and seizing foreign prisoners as a method of strengthening their position in negotiations. In a similar incident in 2019, Iran seized a British tanker and held it for two months.
"We've become used to such allegations," an Iranian government spokesman told reporters. He went on to blame South Korea for the incident: "...it is Korea's government that is holding $7 billion, which belongs to us, hostage on baseless grounds."
South Korea called in Iran's ambassador to demand that the ship be released. Officials said a team was being sent to Iran to discuss the situation. Iran said its forces stopped the ship for violating environmental rules by polluting waters in the Persian Gulf.
However, an official with DM Shipping Company, the ship's owner, denied the tanker was polluting the waters, The Associated Press reported.
Iran's threat to block shipping in the Gulf is one way to gain leverage in its expected negotiations with the administration of President-elect Joe Biden.
South Korea, like other countries, is required to limit Iran's access to its financial system under U.S. sanctions. The restrictions were ordered by the administration of U.S. President Donald Trump. The United States placed strong restrictions on Iran after it withdrew from a nuclear agreement reached with Iran under former president Barack Obama.
Biden has said he wants to reenter the nuclear agreement. But doing so is likely to present diplomatic problems. Since the United States withdrew from the deal, Iran has taken steps that violate it. Biden said Iran must fully obey the agreement in order for the deal to be saved.
Iran has said the United States must first lift the sanctions. Iranian officials say the sanctions are illegal and have hurt its economy, including its ability to deal with the highest number of COVID-19 cases in the Middle East.
In another development, Iran announced Monday it had increased uranium enrichment at an underground production center. That is its latest move to violate the former nuclear deal's terms.
South Korea's Foreign Minister, Kang Kyung-wha, said on Tuesday she was making diplomatic efforts to secure the release of the tanker. South Korea's Vice Foreign Minister, Choi Jong-kun, is expected to visit Iran on Sunday. A government official in Tehran told Iranian state TV the visit had already been planned to discuss the frozen money.
I'm Bryan Lynn.