TEHRAN, Iran (AP) — The sailors from a South Korean tanker seized in the Persian Gulf by Iranian troops last month are free to leave the country on humanitarian grounds, Iran’s state TV said Tuesday.

Foreign Ministry spokesman Saeed Khatibzadeh said a legal investigation into the tanker and its captain would continue. Iran maintains the tanker and its 20-member crew were stopped because of the vessel’s “environmental pollution,” a claim rejected by the vessel’s owner.

It appeared the South Korean-flagged tanker’s seizure in the crucial Strait of Hormuz was an attempt by the Islamic Republic to increase its leverage over Seoul ahead of negotiations over billions of dollars in Iranian assets frozen in South Korean banks amid a U.S. pressure campaign targeting Iran. The vessel’s seizure came ahead of South Korea’s pre-scheduled regional trip, which included a stop in Qatar.

The crew, including sailors from Indonesia, Myanmar, South Korea and Vietnam, were in custody at the port city of Bandar Abbas near the Strait of Hormuz. The report did not say whether the captain will be allowed to leave the country or when the sailors might actually be released.

Khatibzadeh said Deputy Foreign Minister Abbas Araghchi spoke by phone Tuesday with South Korean First Vice Foreign Minister Choi Jong-Kun and the two discussed the issue of the release of Iran’s frozen assets.

Jong-Kun and his delegation visited Tehran last month to discuss the release of the ship and crew and some $7 billion in frozen Iranian assets tied up in the country’s banks due to American sanctions.

Iran’s foreign minister had told the visiting South Korean delegation that the release of its vessel and crew was a matter for the courts and out of the government’s hands.