An Iranian-flagged tanker was confiscated by the United States earlier this year in Greek and was seen reloading in the country after authorities approved the release of the cargo, sources familiar with the matter said on Friday.

Iran PressEurope: The case has strained relations between Athens and Tehran amid growing tensions between Iran and the United States after Washington hired a tanker in April to impound the oil onboard the Lana tanker, which had been anchored off Greece.

Reuters quoted an unnamed Greek source saying that the U.S. Department of Justice had confiscated 700,000 barrels of the Iranian oil cargo.

The source said that the oil cargo had been transferred to another ship hired by Washington and would be sent to the U.S. 

At the time, the PMO described the U.S. seizure of the Iranian oil cargo as an "act of piracy" that was "in violation of international standards." The Iranian Foreign Ministry also condemned the unacceptable surrender of Greece to illegal U.S. pressures and reiterated that the seizure was an example of international piracy.

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The seizure of the Iranian oil tanker took place at a time when the U.S. administration claimed it sought the revival of the Joint Comprehensive Plan of Action (JCPOA), commonly known as the Iran deal. So far, talks for the resurrection of the 2015 deal have come to a standstill.

Iran's Islamic Revolution Guards Corps (IRGC) seized two Greek oil tankers in the Persian Gulf over violations in May.

Tehran and Athens had friendly relations before the unilateral U.S. imposition of sanctions against Iran and countries working with it. The export of Iran's oil to Greece was halted due to the bans.

"The transfer has started," said a source with knowledge of the matter, on condition of anonymity.

A second source said the transfer process started on Friday and was expected to be completed in days.

There was no immediate response from Iran on Friday, which had previously warned of "punitive action" against Athens over the confiscation.

In July, a U.S. State Department spokesperson said that Washington was "respectful that this case went through the Greek judicial process."

Claire Jungman, chief of staff with U.S. advocacy group United Against Nuclear Iran, which monitors Iran-related tanker traffic through the ship and satellite tracking, said Greece, as a U.S. ally, "had an opportunity to take a stance."

"Instead, this decision by the Greek courts tells Iran that there are no repercussions for its hijacking of tankers," Jungman told Reuters.

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