DUBAI, United Arab Emirates — Iran’s paramilitary Revolutionary Guard says it has seized two Greek oil tankers in the Persian Gulf.

The Guard’s statement on Friday night said the ships were seized over unspecified violations. It did not elaborate.

The U.S. Navy’s Mideast-based 5th Fleet had said it was investigating earlier reports that Iran seized two Greek tankers.

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

THIS IS A BREAKING NEWS UPDATE. AP’s earlier story follows below.

DUBAI, United Arab Emirates (AP) — The U.S. Navy’s Mideast-based 5th Fleet said Friday it was “looking into” reports that Iran had seized two Greek oil tankers after Tehran threatened to take “punitive action” against Athens over a seizure of one of its tankers.

Cmdr. Timothy Hawkins of the 5th Fleet told The Associated Press that the Navy was continuing to investigate. He did not elaborate.

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 Persian 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.

The crude oil cargo of an Iranian-flagged tanker that was stopped in Greek waters last month has been seized and is being transferred to another vessel following a request from the United States, a Greek official said Thursday.

The official said following a “judicial intervention by U.S. authorities concerning the ship’s cargo” the process is currently underway, at U.S. government expense, for the oil “to be handed over” off the port of Karystos on the Aegean Sea island of Evia.

The official, who asked not to be identified in order to discuss the case, did not provide further details. A Justice Department spokesman in Washington and the U.S. Embassy in Athens declined to comment Thursday.