An oil tanker seized by Iran April 27 was carrying Kuwaiti crude and had a crew of 24 Indians, according to the operator.

The U.S. has demanded the immediate release of the Marshall Islands-flagged Advantage Sweet, which was traveling in international waters and near the Gulf of Oman when the incident happened, according to the U.S. military.

The ship was heading to the U.S., a spokesperson for Advantage Tankers, the vessel’s Turkey-based operator, said to Bloomberg April 28. It was carrying oil and was chartered by Chevron Corp., the spokesperson confirmed.

Read more: U.S. Demands Iran Release Oil Tanker Seized in Gulf of Oman

The seizure underscores continued tensions in a vital corridor for oil tankers. Hundreds sail through the Gulf of Oman each month, on their way to and from the Persian Gulf and some of the world’s biggest oil-exporting nations such as Saudi Arabia, Iraq and Kuwait.

Iran’s state-run IRNA news agency said a Marshall Islands-flagged tanker collided with an Iranian vessel in the Persian Gulf, prompting Iran’s navy to seize the vessel and direct it to its coastal waters.

Some U.S. officials believe the move was a retaliation against a decision by the Department of Justice earlier in April to force a tanker headed to China with Iranian oil to redirect to America, the Financial Times reported.

The U.S. has said in recent months that it will do more to enforce sanctions on Iranian energy exports. Iran has a history of seizing tankers after Western nations target its shipments.

Chinese Owner

Advantage Tankers said it’s liaising with insurers and “all the appropriate authorities” to get the ship and crew released.

“The safety and welfare of our valued crew members is our number one priority,” it said April 27. “Similar experiences show that crew members of vessels taken under such circumstances are in no danger.”

The tanker is a Suezmax-class vessel, capable of hauling a million barrels of oil. It loaded a cargo of Eocene crude in the so-called Neutral Zone between Kuwait and Saudi Arabia, according to data compiled by Bloomberg and Vortexa Ltd. 

The tanker most recently signaled South Africa, and its draft indicates it wasn’t completely full, according to the last satellite location received April 27. Its owner is listed as SPDB Financial Leasing, part of China’s Shanghai Pudong Development Bank.