Iranian security forces seized a foreign ship attempting to smuggle fuel out of the country, state media of the Islamic Republic reported on Wednesday.

They detained the crew on the ship, which was reportedly carrying more than 550,000 liters of smuggled fuel. The vessel was escorted from Gulf waters into the harbor and is under investigation by authorities, reported Reuters.

“We were able to identify and detain a ship carrying fuel intended to transport large-scale smuggled shipments east of Maru Island,” said the chief of provincial border guards, Hossein Dehaki.

Other ships attempting to do the same have been captured in recent months, according to reports which point to the cause as being U.S.-imposed sanctions on Iranian oil exports.

According to a report in The Washington Post earlier this year, smuggling often occurs at night. The Iranian ships draw as close as 14 to 20 miles off the coast of the United Arab Emirates and switch off their automatic identification system so they cannot be tracked.