The decision was made while talks are underway in Vienna between Tehran and other world powers to salvage the regime's 2015 nuclear deal and lift US sanctions on the Islamic Republic.
Iran released a South Korean-flagged tanker on Friday, seized in January when Iranian authorities are pressuring Seoul to unlock several billion dollars frozen by US sanctions.
The release comes as talks occur in Vienna between Tehran and other world powers to try to salvage the 2015 Iranian nuclear deal and lift US sanctions on the country.
According to the South Korean Foreign Ministry, seized in January by the Revolutionary Guard, the ideological army of Tehran, the oil tanker "Hankuk Chemi" "left today safe and sound," and its captain was released.
"The prosecutor ordered the release of the ship after the completion of the investigation (and) at the request of the ship's owner and the South Korean government," Iran's Foreign Relations spokesman Said Khatibzadeh later confirmed, quoted by the official Irna agency.
"The lack of antecedents in the region on the part of the captain and the ship" led the prosecutor to make the decision, Khatibzadeh added.
Websites that track the vessels indicate that the 147-meter-long tanker is heading for the Strait of Hormuz.
At the time of the tanker's seizure, Tehran accused the ship, which was carrying 7,200 tons of "petroleum-derived chemicals", of maritime pollution, and the twenty crew members were detained.
In February, Iran allowed all crew members except the captain to leave the country for "humanitarian" reasons. Still, most of them remained on board to maintain the tanker.
Iran was one of South Korea's main oil suppliers until Seoul halted its purchases in 2018 after the United States, under former President Donald Trump, decided to exit the international nuclear deal with Iran.
Tehran accused Seoul of holding $ 7 billion in Iranian-owned funds "hostage." Still, it repeatedly denied that the seizure of the tanker is related to this issue.
Negotiations in Vienna
Current US President Joe Biden said he was willing to salvage the deal on Iran's nuclear program. This week negotiations began between the international community and Iran in Vienna to this end.
South Korea announced in March that it had come up with a solution to unlock the funds but was waiting for the green light from Washington.
US Secretary of State Antony Blinken had said that Washington was opposed unless the Islamic Republic once again respected the international agreement on its nuclear program.
The South Korean Foreign Ministry made no mention of these funds in its statement on Friday.
On the part of the shipowner, DM Shipping, no one wanted to comment at first.
According to various South Korean media, Prime Minister Chung Sye-Kyun will soon travel to Tehran.
The seizure of "Hankuk Chemi" was the first by Iranian forces in more than a year.
The Guardians of the Revolution intercepted the British-flagged tanker "Stena Impero" in the Strait of Hormuz in July 2019, through which a fifth of world oil production transits, before releasing it a month later.
The arrest of the "Stena Impero" was then interpreted as a response to the British authorities in Gibraltar of an Iranian oil tanker released despite American objections.
Tehran has dismissed any connection between the two incidents.
Iranian forces have seized at least six other vessels this year for alleged fuel smuggling.