The U.S. demanded that Iran release an oil tanker siezed while hauling crude through the Gulf of Oman, the latest flare-up in one of the world’s important waterways. 

Iran’s navy seized the Marshall Islands-flagged Advantage Sweet in international waters at about 1:15 p.m. local time April 27, according to the U.S. Navy. The vessel issued a distress call, and the U.S. Fifth Fleet is monitoring the situation. 

“Iran’s actions are contrary to international law and disruptive to regional security and stability,” the U.S. said. “The Iranian government should immediately release the oil tanker.”

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

The incident highlights continued tensions in a vital corridor for oil transport. Hundreds of tankers sail through the Gulf of Oman each month, on their way to and from the Persian Gulf and the Middle East’s biggest oil-producing nations. In recent years, tensions among governments in the region have heightened the risk for ships, with some even turning off their transponders as they navigate around the Arabian peninsula.

The Advantage Sweet, which loaded earlier in April in the zone shared by Saudi Arabia and Kuwait, was chartered by Chevron Corp. to haul oil to the U.S., data compiled by Bloomberg show. 

A Chevron spokesperson said the company is monitoring the situation. “We are in contact with the vessel operator with the hope of resolving this situation as soon as possible,” the company said in a statement. 

The Pentagon initially said Iran’s Islamic Revolutionary Guard Corps conducted the seizure, but have since stated that the Iranian navy did so. 

Since 2021, Iran has seized at least five commercial vessels in the Middle East, according to the U.S. The Fifth Fleet said it didn’t have any contact with the Advantage Sweet’s crew after the distress signal, and officials weren’t aware why it was seized or where it had been taken. 

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 Shanghai Pudong Development Bank.