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 United States from a tanker held off the Greek coast.

Iran’s Revolutionary Guard (IRGC) said in a statement on their official website on Friday that they seized two Greek oil tankers in the Arabian Gulf “due to violations that were committed.” The statement did not elaborate on what the “violations” were.

Greece responded by accusing Iran of “piracy” after the IRGC said they seized two Greek-flagged oil tankers in the Gulf Friday.

“These actions are tantamount to acts of piracy,” the foreign ministry said in a statement, warning Greek citizens to avoid travelling to Iran. It said it had strongly protested to the Iranian ambassador in Athens against the “violent” seizure.

The move came amid a dispute between the two nations about the fate of an Iranian oil cargo on board a Russian-flagged tanker that was seized in Greece in April.

Athens said Iranian navy helicopters had landed armed men on the two tankers earlier on Friday.

One of them, the Delta Poseidon, was sailing in international waters at the time, the ministry said.

A spokeswoman at the Athens-based company Polembros identified the second tanker as the Prudent Warrior.

“The ship has been seized by the Iranian authorities. We have no communication with them at this time,” she told AFP.

The Greek foreign ministry said the second tanker was near the Iranian coast when seized.

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

Athens has informed the European Union and the International Maritime Organisation of the incident, the ministry said.

Escalating tensions

On Wednesday, Greece said it would send 115,000 tonnes of Iranian oil from the tanker seized in April to the United States at the request of the US Treasury, which oversees the enforcement of sanctions on Iran.

Iran’s foreign ministry demanded earlier on Friday that Greece release the vessel, saying the planned transfer of its cargo to the US was a “clear violation” of international law.

Athens has linked the tanker seizure in Greece to sanctions imposed on Russia following its invasion of Ukraine in February.

The Iranian foreign ministry earlier this week summoned the Greek charge d’affaires to protest.

Iran’s foreign ministry also summoned the Swiss charge d’affaires, whose country has handled US interests in Iran ever since ties were cut between Tehran and Washington following the 1979 revolution.

The ministry protested “the US government’s pressure and intervention” that led to the seizure of the ship by Greek authorities last month.

EU member Greece said at the time it was enforcing sanctions the bloc had imposed on Russia following its invasion of Ukraine in February.

Iran accused the US of a “clear violation of the law of the sea and the relevant international conventions” and “called for the immediate lifting of the seizure of the ship and its cargo”.

The row over the tanker has taken place against the backdrop of tense efforts to revive the 2015 nuclear deal between Iran, the US and several other world powers.

The US reimposed crippling sanctions on Iran after then-President Donald Trump pulled out of a nuclear agreement between Tehran and major powers in 2018.