ΤΕΗΕRΑΝ – Iran’s paramilitary Islamic Revolutionary Guard Corps (IRGC), which seized two Greek tankers, said there could be further retaliation and more ships held over Greece aiding the United States in confiscating Iranian oil from a ship.

No more details were immediately available, said Kathimerini, noting that Iran said it would take “punitive action” against Greece, which has called for the release of the detained tankers and crews in what it said was an act of piracy.

The action appeared to be retaliation for Athens’ assistance in the U.S. seizure of crude oil from an Iranian-flagged tanker in the Mediterranean Sea over violating Washington’s crushing sanctions on the Islamic Republic.

The raid marked the first major incident at sea in months as tensions remain high between Iran and the West over its tattered nuclear deal with world powers. As Iran enriches more uranium, closer to weapons-grade levels than ever before, worries mount that negotiators won’t find a way back to the accord – raising the risk of a wider war.

The Guard issued a statement announcing the seizures, accusing the tankers of unspecified violations. Nour News, a website close to Iran’s Supreme National Security Council, warned Greece would be punished for assisting the U.S. in seizing oil days earlier from the Iranian-flagged tanker Lana.

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.

The ministry called for the release of the vessels and their crews, warning the seizure would have “particularly negative consequences” in bilateral relations and in Iran’s relations with the European Union, of which Greece is a member.

An Iranian helicopter landed on the Greek-flagged Delta Poseidon in international waters 22 nautical miles off the coast of Iran, the ministry said. “Armed men then took the crew captive,” it said, adding two Greek nationals were among the crew.

“A similar incident has been reported on another Greek-flagged vessel, that was carrying seven Greek citizens, close to the coast of Iran,” the ministry statement also said in a threat.

A Greek official, speaking on condition of anonymity to discuss details of the attack with a journalist, identified the second ship as the Prudent Warrior. Its manager, Polembros Shipping in Greece, earlier said the company was “cooperating with the authorities and making every possible effort to address the situation effectively.”

(Material from the Associated Press was used in this report)