U.S. Central Command confirmed Monday that the two Greek ships were in international waters when they were controlled by the IrGC.
During a telephone conversation with his Greek counterpart, U.S. Secretary of State Anthony Blinken condemned Iran's takeover of the two oil tankers.
Blinken said Irans continued harassment of ships poses a threat to maritime security and the global economy, calling on Iran to immediately release the two Greek oil tankers.
The IRGC released a video documenting the seizure of Greek oil tankers by navy personnel in gulf waters.
Last Friday, the Revolutionary Guard announced the detention of two Greek oil tankers in the Gulf for "violating navigation rules and assets."
On Sunday, France called on Iran to immediately cease its actions contrary to international law.
The French Foreign Ministry condemned Iran's hijacking of two Greek ships in the Gulf waters.
Earlier, the EUROPEAN Union expressed deep concern about Iran's detention of two Greek ships in Gulf waters, calling on Tehran to de-escalate.
"We have expressed our deep concern to the Iranian authorities about these actions, and we call for speedy clarification, resolution and de-escalation," the union said in a statement.
The statement stressed that freedom of navigation and the flow of trade were fundamental principles supported by the European Union.
Iran confirmed on Saturday that the crew members of the two tankers were "in good health," noting that they were still on board the ships and had not been arrested.
Iran confirmed on Saturday that the crew members of the two tankers were "in good health," noting that they were still on board the ships and had not been arrested.
For its part, the Greek Foreign Ministry accused Iran of "piracy,"noting that nine of its citizens are on the crew of the two ships, refusing to specify the number of other sailors.
This comes amid strained relations between Tehran and Athens after the latter announced that it would deliver Iranian oil to the United States on board a russian-flagged tanker.
The two Greek carriers seized were Prudent Warrior and Delta Poseidon
One tanker was seized near Asalawia and the other near Bandar Langa near Hendurabi Island.
Greece detained an Iranian-flagged ship last month, while media reported that Greece had delivered oil to the United States.
The Greek government has warned all Greek ships sailing in the Gulf to "adapt to the unacceptable situation, the reality of the Iranian government's tactics," following Iran's seizure of two Greek oil tankers last week, the spokesman said.
On behalf of the government, Iwanis Oiconomo, for journalists in Athens.
Bloomberg news agency reported Monday that the seizure of Iranian oil in Greece was the result of international agreements signed by the state, Greece's commitments, and court decisions.
Iran had time to appeal, or to demand a stay of the court's decision, but this did not happen.