Iran released a South Korean oil tanker and its captain, Seoul's foreign ministry said Friday, about three months after they were seized over alleged oil pollution.

The ship, with its captain and 12 other crew members aboard, left the port near Bandar Abbas on the southern coast, at around 6 a.m. (Iran time), the ministry said. The crew members had been released earlier but have remained on the ship for maintenance purposes.

The ministry said the captain and the crew members remain safe and sound.

Iran's Islamic Revolution Guards Corps seized the Hankuk Chemi and its 20 crew members in its waters on Jan. 4, claiming that the ship violated environmental rules.

But speculation has persisted that the seizure was linked to Tehran's anger over what it sees as Seoul's lack of efforts to release about $7 billion of Iranian assets locked in South Korean banks due to US sanctions.

Iran has said the seizure is purely a technical issue to be dealt with in accordance with judicial procedures.

The release came amid speculation that Seoul and Tehran might have made headway in addressing the Middle Eastern country's call to unlock the funds, although neither side has acknowledged that the ship seizure and the frozen funds are related.

The two countries have been in consultations to resolve the issue of the frozen money, including using a US-backed Swiss humanitarian trade arrangement to facilitate the export of humanitarian goods to Iran.

Using the money to pay off Iran's UN dues in arrears has also been among the payment methods being discussed.

"We're expecting to make a considerable progress in terms of paying the UN dues," a foreign ministry official said. "We have also exported some $30 million worth of medical equipment since we resumed the humanitarian trade with Iran last April."

Seoul has also closely consulted about the frozen funds with the US and European partners, the countries that are undergoing negotiations with Tehran to restore a 2015 nuclear deal aimed at limiting Iran's nuclear activities, the official added.

"If the JCPOA talks move forward, we think that it could have a positive effect on the frozen funds issue," he said.

Meanwhile, the ship's release was decided after the Iranian authorities and the vessel's Korean operator reached a settlement. Tehran had never begun any legal proceedings against the ship, according to the official.

Since February, the captain and a few crew members have stayed on the ship after the Iranian authorities announced they would set free all sailors except for the captain for the ship's management. (Yonhap)