The action was taken to be a response to Greece's role in the earlier U.S. seizure of crude oil from an Iranian-flagged tanker in the Mediterranean Sea.

Tensions are high following the first major incident at sea in months. Tehran continues to enrich Uranium, bringing it closer to weapons-grade levels.

The Guard issued a statement announcing the seizures of the Greek vessels, leveling unspecified accusations at the tankers. Shortly before the seizures took place, Nour News, a website close to Iran's Supreme National Security Council, warned that Tehran planned to take "punitive action" against Greece.

Greece's Foreign Ministry said it made a strong demarche to the Iranian ambassador in Athens over the "violent taking over of two Greek-flagged ships" in the Persian Gulf. "These acts effectively amount to acts of piracy," a ministry statement said.

The ministry demanded the immediate release of the vessels and their crews, warning that the seizure would have "particularly negative consequences" not only in bilateral relations, but in Iran's relations with the European Union, of which Greece is a member.