GIBRALTAR - An Iranian oil tanker seized in Gibraltar for violating EU sanctions sailed from Gibraltar's waters Sunday after the British colony's Supreme Court rejected repeated U.S. requests to turn over the vessel suspected of intending to deliver crude to Syria.

Marine traffic monitoring data indicated Monday the tanker - with its named changed from Grace 1 to Adrian Darya 1 - was making its way to a port in Greece, though officials have not publicly confirmed its destination.

The Gibraltar government said it had received a "supplemental request" from the United States as late as Saturday to stop the tanker from leaving Gibraltar waters, where it had been anchored for 46 days with 2.1 million barrels of oil on board. But authorities were "unable to seek a Supreme Court Order to provide the restraining assistance requested," the statement said.

Initial U.S. requests to hold the vessel were rejected by Gibraltar's high court last Thursday. The colony's chief minister Fabian Picardo said that Iran had given assurances that the oil would not go to Syria, a destination prohibited by EU sanctions against the government of Bashar al-Assad.

Subsequent U.S. requests were based on offenses under the International Emergency Economic Powers Act linked to U.S. sanctions against Iran that do not apply in Gibraltar, Britain or the rest of the European Union, according to the Gibraltar Justice Ministry.

Iranian Foreign Ministry spokesman Abbas Mousavi told reporters Monday that Iran had warned the United States through official channels against making any new attempt to seize the tanker.

U.S. pressures were also exerted directly on the British government by top Trump administration officials including National Security Adviser John Bolton who flew to London last week.

"There is no embargo policy against Iran in EU countries," said Gibraltar attorney Joseph Triay. He said that the ship should have been allowed to sail last week.

Sources close to the Gibraltar attorney general's office say that the United States alleged that proceeds from the tanker's oil deliveries were going to companies associated with Iran's Revolutionary Guard, which the U.S. State Department recently designated as a terrorist organization.

Some analysts say the tanker's release could also be the start of an exchange with the Iranian government, which seized British-flagged tanker Stena Impero as it entered the Persian Gulf last month. Iran's Guardian Council spokesman Abbas Ali Kadkhodaei has called the ship's boarding by the Revolutionary Guard a "reciprocal move."

"There is much speculation that the release of Grace 1 is a pre-condition for the Iranian regime to release the British ship Stena Impero," said Benjamin Weinthal of the Washington-based Foundation for Defense of Democracies.

'Escalation of tensions'

The seizure of yet another British tanker was narrowly averted by a Royal Navy frigate that blocked three Iranian patrol boats approaching the vessel. Britain's Foreign Office called the incident an "escalation of tensions."

The Royal Navy announced that it was reinforcing its presence in the Persian Gulf with a destroyer diverted from NATO duties in the Black Sea, which would raise its total number of warships in the Gulf area to two.

American defense journalist David Axe says the Royal Navy is too "overstretched" to effectively protect the volume of British tanker traffic moving through the Strait of Hormuz.

The United States has an aircraft carrier task force deployed in the Gulf to protect its shipping interests.

The British Foreign Office refuses to link the seizing of the Stena Impero with that of the Adrian Darya 1 and denies that any negotiations are underway with Tehran.

But last week, an Iranian port official said that documents were being exchanged between London and Tehran which indicated that the "problem would be resolved in the near future."