TEHRAN, Iran — Iranian authorities have detained 18 crew members, including the ship’s captain, after seizing a foreign tanker in the Gulf of Oman that officials say was transporting millions of liters of smuggled fuel, state-affiliated media reported Saturday.

The vessel was intercepted Friday and found to be carrying about 6 million liters of fuel, according to reports citing the judiciary in Iran’s southern Hormozgan province. Officials did not identify the tanker or disclose the nationalities of those aboard.

Authorities said the ship is suspected of multiple violations, including failing to comply with orders to stop, attempting to escape interception, and operating without proper navigation and cargo documentation. An investigation into the case is ongoing.

Iran has stepped up enforcement against fuel smuggling in recent years, driven by heavily subsidized domestic fuel prices and a sharply weakened national currency. Officials say illicit fuel is frequently moved overland to neighboring countries and by sea to Gulf Arab states.