Iran has seized a foreign tanker with 12 crew in Lark Island in the Persian Gulf amid growing tensions between the Middle Eastern nation and the West. Iranian state TV said the Revolutionary Guards took the action after the tanker was taking fuel from Iranian smugglers to foreign customers.

The tanker was reportedly intercepted south of Iran’s Larak Island in the Strait of Hormuz, an important oil shipping route. The identity of the tanker remains unknown. It was also not revealed which country the crew was from. The guards confirmed the seized vessel was the same one it towed on Sunday after it sent a distress call.

Earlier, U.S. officials raised concerns about a Panamanian-flagged oil tanker, Riah, which stopped transmitting its location over the weekend, may have been seized in Iranian territorial waters. This oil tanker, based in the United Arab Emirates, disappeared off trackers in Iranian national waters. An Emirati official said the tanker made no distress call before switching off its tracker, according to Sky News.

The latest action comes as tensions mount between the U.S. and Iran over the unraveling nuclear deal between Tehran and world powers, and the seizure of an Iranian ship by Gibraltar authorities.

An Iranian official had threatened to seize British tankers in retaliation and last week Iranian gunboats reportedly tried to "impede" a British tanker, forcing a Royal Navy ship to warn them off. Britian has sent more naval ships into the region following that incident.