Iran has released a South Korean oil tanker it seized three months ago amid a dispute over billions of dollars in funds frozen due to U.S. sanctions.

South Korea’s Foreign Ministry said in an April 9 statement that the Hankuk Chemi and its captain had been released and the vessel left an Iranian port near Bandar Abbas. Twelve of the crew who had previously been released stayed on the ship for maintenance while it was impounded.

Iran’s Islamic Revolutionary Guards Corps (IRGC) seized the Hankuk Chemi on January 4 near the Strait of Hormuz. At the time of its seizure, Iran said the vessel was leaking oil in violation of environmental laws.

The move was widely considered a response to around $7 billion frozen in Iranian bank accounts in South Korea, although Tehran officially denied its actions had anything to do with the money.

The United States reimposed sanctions on Iran in 2018 after former President Donald Trump withdrew Washington from the 2015 nuclear deal between Tehran and world powers.

South Korea was a major buyer of Iranian oil until Washington ended a sanctions waiver on the Asian economy’s imports of Iranian oil in 2019. That left the Iranian funds sitting frozen in two South Korean banks.

South Korea’s Foreign Ministry made no mention of any deal or the funds. But in February the two sides agreed to speed the way forward for Iran to receive its money pending U.S. approval. Iran has said it needs the money so it can purchase medicine, medical equipment, and COVID-19 vaccines.

The development comes as negotiators from Iran and world powers have been meeting in Vienna to overcome an impasse over U.S. sanctions on Iran and Iranian breaches of the nuclear agreement.