Iranian forces seized two Greek tankers in the Gulf on Friday, Iranian state media reported, shortly after Tehran warned it would take “punitive action” against Athens over the confiscation of Iranian oil by the US from a tanker held off the Greek coast.

“The Revolutionary Guards Navy today seized two Greek tankers for violations in Gulf waters,” said a Guards statement, quoted by the state news agency IRNA.

It gave no further details or say what the alleged violations were.

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 Arabian Gulf.

“These actions are tantamount to acts of piracy,” the foreign ministry said in a statement, warning Greek citizens to avoid traveling to Iran.

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

The ministry’s statement said that earlier Friday, an Iranian helicopter landed on the Greek-flagged Delta Poseidon in international waters some 22 nautical miles off the coast of Iran.

“Armed men then took the crew captive,” it said, adding that 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 said.

It added that one of the vessels was the Delta Poseidon, while a spokeswoman at the Athens-based company Polembros identified the second tanker as the Prudent Warrior.

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 owner, Polembros Shipping in Greece, earlier said the company was “cooperating with the authorities and making every possible effort to address the situation effectively.”

The ministry said nine Greeks were among the crews of both vessels, but did not give a number of other sailors on board.

A US defense official, speaking on condition of anonymity to discuss intelligence matters, said it appeared the two ships had come close to — but not in — Iranian territorial waters Friday before drifting off into Iranian waters. The ships also had turned off their tracking devices, another red flag, the official said. However, neither had issued a mayday or a call for help, the official said.

Iran had threatened to take “punitive action” earlier Friday over Athens being involved in the US seizure of an Iranian oil tanker in Greek waters.

Iran’s Nour News website, close to its security services, made the threat just as shipping news site Lloyd’s List said it believed two Greek tankers had been seized in the Arabian Gulf. Quoting anonymous industry sources, Lloyd’s reported that the two ships had been boarded after Iranian military helicopters approached them on Friday afternoon. It said both tankers had just been loaded with Iraqi crude oil.

Greek authorities last month impounded the Iranian-flagged Pegas, with 19 Russian crew members on board, near the coast of the southern island of Evia due to EU sanctions.

Washington later confiscated the Iranian oil cargo held onboard and plans to send it to the United States on another vessel, Reuters reported on Thursday.

The Pegas was later released because of confusion about the sanctions over its owners.

The Pegas was among five vessels designated by Washington on Feb. 22 — two days before Russia’s invasion of Ukraine — for sanctions against Promsvyazbank, a bank viewed as critical to Russia’s defense sector.

It was unclear whether the cargo was impounded because it was Iranian oil or due to the sanctions on the tanker over its Russian links. Iran and Russia face separate US sanctions.

Also on Friday, Iran summoned an envoy of Switzerland, which represents US interests in Tehran, to protest against the Pegas oil seizure, the Iranian foreign ministry said.

“The Islamic Republic expressed its deep concern over the US government’s continued violation of international laws and international maritime conventions,” state media quoted the foreign ministry as saying.

A spokesperson for the US Department of Justice declined to comment on the oil seizure.

IRNA quoted Iran’s Ports and Maritime Organization as saying the tanker had sought refuge along the Greek coast after experiencing technical problems and poor weather. It called the seizure of its cargo was “a clear example of piracy.”

The US on Wednesday imposed sanctions on what it described as a Russian-backed oil smuggling and money laundering network for Iran’s Revolutionary Guards’ Quds Force.

In 2019, Iran seized a British tanker near the Strait of Hormuz for alleged marine violations two weeks after British forces detained an Iranian tanker near Gibraltar, accusing it of shipping oil to Syria in violation of European Union sanctions. Both vessels were later released.

(With Reuters, AP and AFP)