Iran’s Foreign Ministry summoned Wednesday the Greek chargé d'affaires to protest the seizure of a vessel carrying Iranian crude oil in Greece's territorial waters.

The ministry said it notified the Greek envoy of his country's "international obligations" regarding the vessel's emergency stop due to a technical difficulty.

The Russia-flagged aframax Lana, formerly named Pegas, was detained on April 15 by Greek authorities and had been waiting at Karistos port pending a court ruling. On Monday afternoon, a tanker owned by Dynacom Tankers Management, called Ice Energy, was chartered by the US Department of Justice and started a ship-to-ship transfer of the US-sanctioned Iranian crude on the basis of Russian sanctions.

The operation, first reported by watchdog group United Against Iran, was verified using Lloyd's List intelligence data.

The head of the Mediterranean and East European affairs at the Iranian ministry condemned Greece’s "unacceptable" surrender to "illegal" US sanctions, saying the "seizure of the cargo of the ship with the flag of the Islamic Republic of Iran was an example of international piracy."

Lana, which arrived off Greece early in April with reports of a possible mechanical failure and anchored south of the Greek island of Evia, was identified as the Russian-flagged Pegas and the assumption at the time was that it was laden with Russian crude.

"The seizure came at the request of the Americans because the cargo came from a sanctioned country and moved on a sanctioned ship," a Greek official told Dow Jones on Wednesday.