Iran's Islamic Revolutionary Guards Corps (IRGC) says it has seized two Greek oil tankers in the Persian Gulf.
The vessels were seized a day after Athens assisted the United States in seizing an Iranian oil tanker over alleged sanctions violations.
The IRGC’s press service on May 27 said it seized the Greek ships “due to violations” that were not specified, according to the Tasnim news agency.
The U.S. Navy said earlier it was looking into reports that Iran seized two Greek tankers after Tehran threatened to take “punitive action” against Athens over the seizure of its tanker.
The Greek Foreign Ministry summoned the Iranian ambassador and lodged a protest, according to a spokesperson.
The ministry said Iranian helicopters landed commandos on the two tankers. One of them, the Delta Poseidon, was sailing in international waters at the time, the ministry said. The other, the Prudent Warrior, was near the Iranian coast when it was seized, the ministry said.
"These actions are practically piracy," the Greek Foreign Ministry statement said.
Greece demanded the immediate release of the crews and that the ships be allowed to continue on their journeys.
News reports on May 26 quoting Greek sources said the United States had confiscated Iranian oil held on a Russian-operated ship near the Greek island of Evia in the Aegean Sea.
An unidentified Greek official quoted by the AP said the process of turning over the oil began after a “judicial intervention by U.S. authorities concerning the ship’s cargo.”
The vessel was temporarily seized by Greek authorities on April 15 when it anchored off the port of Karystos on Evia. At the time, it was flying a Russian flag and was carrying a crew of 19 Russians.
The Greek Coast Guard said it was seized due to suspicions it had breached EU sanctions imposed against Russia due to the war in Ukraine.
It was unclear whether the oil was confiscated because it was Iranian oil subject to U.S. sanctions or whether the action was due to the sanctions on the tanker, which recently changed its name from Pegas to Lana and which has been flying the Iranian flag since May 1.
A source at Greece's Shipping Ministry quoted by Reuters said the U.S. Department of Justice had "informed Greece that the cargo on the vessel is Iranian oil."
The seizures come amid heightened tensions over the Iran nuclear deal and concerns that negotiations to revive the accord will fail.