France has denounced Iran's seizure of two Greek-flagged oil tankers in Persian Gulf waters, urging the Islamic Republic “to immediately release the crews and vessels."

In a statement on Sunday, a French foreign ministry spokesperson described the move as "a serious violation of international law."

"France reiterates its commitment to the rules of international law protecting the freedom of navigation and maritime safety. We call on Iran to immediately cease its actions that contravene these rules," the statement added.

The European Union also issued a statement on Sunday to express its serious concern to the Islamic Republic's authorities following the capture of the oil tankers, and called for transparency, de-escalation and a fast resolution of the issue.

Greece has also condemned Tehran's detention of the two ships as "tantamount to acts of piracy" and warned its citizens not to travel to Iran.

On Friday, Iran’s Revolutionary Guard seized the tankers in helicopter-launched raids in the Persian Gulf about a week after the confiscation of Iranian oil from a tanker held off the Greek coast and its transfer to the US. 

Iran said on Saturday that the crew of two Greek tankers had not been detained and are on board their vessels.

The Greek tankers are Delta Poseidon and Prudent Warrior, and were captured near Asalouyeh off the coasts of Iran’s Bushehr Province and the Hendurabi island near Bandar Lengeh in Hormozgan province, respectively.