"The (Greek) Supreme Court's ruling... is in Iran's favor," a Greek government official said, asking not to be named due to the sensitivity of the issue.
The official said the ruling, which has not been made public, had come to the government's knowledge on Tuesday.
Another official confirmed the ruling. A government spokesperson said the government would not comment on court decisions.
Greek authorities approved its release earlier this month, after a judicial panel ruled in favor of an Iranian company, overturning a previous court order, and the vessel which had engine problems was tugged to Piraeus.
Greek media reported that the United States challenged that decision bringing the case before Greece's Supreme Court.
Part of the ship's Iranian oil cargo had been transferred to another ship, Ice Energy, which was hired by the United States and is also moored off Piraeus port.
"Lana is expected to get fuel later today and test its engine so that it can start the oil transfer at the end of the week and sail off," the first official told Reuters.
Greek authorities in April impounded Lana and its oil cargo with 19 Russian crew members on board near the coast of Evia, due to sanctions following a legal action by the United States.
The ship was later released due to complications regarding its ownership, but part of the Iranian oil cargo had already been transferred to another ship, Ice Energy, which was hired by the United States and is moored off Piraeus port.
The removal of oil from the Lana prompted Iranian forces last month to seize two Greek tankers in the Middle East Gulf and sail them back to Iran after Tehran warned it would take "punitive action" against Athens.
Following an appeal by an Iranian company on June 7, a Greek judicial panel overturned the initial court order that allowed the confiscation of the cargo on behalf of the United States.
MP/PR