Sekavin SA, a Greek fuel supplier, said it’s investigating the origin of a cargo aboard an Iranian tanker off the Mediterranean island of Syros amid a European Union ban on purchases from the Middle East nation.

The Baikal arrived at the Greek island on Monday and has the capacity to carry about 1 million barrels of oil or refined products, ship-tracking data compiled by Bloomberg show. The cargo of ship fuel hasn’t been unloaded, Sekavin Operation Manager Yannis Spyridakis said by phone on Tuesday. The vessel is flying the Tanzanian flag, he said.

NITC, a Tehran-based tanker operator, controls the ship and says the company is owned by Iranian pension funds, data compiled by Bloomberg show. The 27-nation EU barred imports of Iran’s oil and refined products in July. The EU and U.S. have intensified sanctions, saying the country’s nuclear program is aimed at producing weapons, a charge Iran has denied.

“It’s clear that sanctions are getting tighter and tighter against Iran,” Samuel Ciszuk, an oil consultant at KBC Energy Economics in Walton-on-Thames, England, said by phone Tuesday. “There is great uncertainty for all parties involved as soon as Iran appears in the supply chain because of the embargo and financial sanctions.”

Habib-ullah Seyedan, NITC’s commercial director, declined to comment by phone Tuesday and said the company’s operations manager was not available for comment.

The Baikal arrived in Greece having been off the coast of Morocco as recently as Nov. 11, the ship-tracking data show.

Tanzania-Zanzibar said last month 14 Iranian tankers that were previously registered in Tuvalu were mistakenly signaling the east African territory as their flag state. NITC renamed part of its fleet and changed the ship registrations amid sanctions on Iran’s nuclear program, which the government in Tehran maintains is for civilian purposes.

The EU banned imports of the Middle East nation’s oil in July under legislation that also prohibited any vessel insured in the 27-country bloc from carrying the crude. The U.S. Treasury Department said July 12 it would block transactions through the country’s financial system involving NITC and 27 affiliated entities.

The EU sanctions on Iranian oil affected about 95 percent of the global tanker fleet because the ships are insured under rules governed by European law. Carrying Iranian oil would invalidate ships’ insurance against risks including spills and collisions, according to the International Group of P&I Clubs.

The sanctions are costing Iran about $98.9 million a day based on the average price of the country’s cheapest crude in Asia, its largest market, and October’s export estimates from the International Energy Agency.

[Bloomberg]