The Iranian Revolutionary Guards Corps (IRGC) have detained two Greek oil tankers in the Persian Gulf.

The ships disregarded maritime regulations, the IRGC web portal said on Friday.

More details on the two tankers and crew should be announced soon.

Greece protested in the strongest terms and spoke of an act of piracy.

Observers suspect an act of retaliation behind the action.

Recently, the Russian-flagged tanker "Lana" with Iranian oil on board was arrested in Greek waters.

In protest against this, chargé d'affaires from the Greek and Swiss embassies were summoned to the Foreign Ministry on Friday.

Switzerland also represents US interests in Tehran.

The Greek Foreign Ministry summoned the Iranian ambassador on Friday.

A protest had been filed, said a spokesman.

"These actions are practically piracy," the Foreign Ministry said in a statement in Athens.

Greece demanded the immediate release of the crews.

The ships should be allowed to proceed.

These actions would have "very negative repercussions" on Greek-Iranian relations, according to the Foreign Ministry.

According to information from Athens, the crew of a helicopter of the Iranian Navy boarded the Greek ship "Delta Poseidon" in international waters around 22 nautical miles (around 35 kilometers) off the coast of Iran on Friday.

Armed Iranians then arrested the crew.

A second Greek ship was also stopped and the crew arrested, the Greek Foreign Ministry said.

Athens has informed all relevant international organizations about the incidents and called on all Greek citizens to avoid traveling to Iran, it said.

All Greek ships moving in the Persian Gulf region were also notified.

Greek media such as the Kathimerini newspaper reported on the incident involving the Russian tanker.

Accordingly, on April 14 there was a severe storm in the Aegean.

The "Lana" coming from the Turkish Marmaris sought refuge in a bay of the Greek island of Euboea in front of the small port of Karystos.

There, the Greek authorities established that the tanker belonged to the Russian Promsvyazbank.

Because the EU had imposed sanctions on the bank, the tanker was stopped.

When it became clear that the bank had already sold the tanker to an unsanctioned Russian bank in March, it was supposed to move on.

In the meantime, however, it has been determined that the Russian tanker was transporting Iranian oil.

Therefore, according to the Greek media, US authorities reported and demanded that

that the Greeks provide support and continue to hold the "Lana".

Because of the US sanctions imposed on Iran, the oil should have been pumped onto another tanker and shipped to the US at US expense.

Apparently this is what is happening in the Gulf of Karystos.

The marine portal MarineTraffic shows that another tanker is lying next to the "Lana" in the Gulf of Karystos and, according to all indications, is refueling the oil from the ship.