An Iranian supertanker the U.S. has suspected to be tied to a sanctioned organization has lifted its anchor and started moving away from Gibraltar on Sunday and Iran warned the U.S. not to interfere with its voyage.

The trail left by GPS data on Marinetraffic.com, a vessel-tracking service, showed the Iran-flagged Adrian Darya 1, previously known as Grace 1, moving shortly before midnight. The tanker slowly moved southeast toward a narrow stretch of international waters separating Morocco and the southern tip of the Iberian Peninsula.

Abbas Mousavi, a foreign ministry spokesman, told reporters that any attempt by the U.S. to seize the ship would "endanger shipping safety in open seas. We have issued a warning through official channels, especially the Swiss embassy,” according to Reuters.

The vessel hauling $130 million worth of light crude oil had been detained for a month in the British overseas territory for allegedly attempting to breach European Union sanctions on Syria. Gibraltar rejected an eleventh-hour attempt by the United States to reseize the oil tanker on Sunday, arguing that EU regulations were less strict than U.S. sanctions on Iran.

The vessel’s next destination was not immediately known.

An on-duty officer at the Port Authority of Gibraltar declined to comment to The Associated Press on the ship’s moves and deferred questions to the government. The Gibraltar government press office did not immediately respond to AP messages seeking comment.

Iran’s ambassador to Britain, Hamid Baeidinejad, had announced earlier on Twitter that the ship was expected to leave Sunday night.

Shortly after the tanker’s detention in early July near Gibraltar, Iran seized the British-flagged oil tanker Stena Impero, which the Islamic Republic has continued to hold.

Gibraltar’s government said Sunday it was allowing the Iranian tanker’s release because “the EU sanctions regime against Iran - which is applicable in Gibraltar - is much narrower than that applicable in the US.”

In a last-ditch effort to stop the release, the U.S. unsealed a warrant Friday to seize the vessel and its cargo of 2.1 million barrels of light crude oil, citing violations of U.S. sanctions as well as money laundering and terrorism statutes.

U.S. officials told reporters that the oil aboard the ship was worth some $130 million and that it was destined for a designated terror organization.

The unsealed court documents argued that Iran’s Islamic Revolutionary Guard Corps was the ship’s true owner through a network of front companies.

Authorities in Gibraltar said Sunday that, unlike in the U.S., Iran’s Revolutionary Guard was not designated a terrorist organization under EU, U.K. or Gibraltar law.

Iran has not disclosed the Adrian Darya 1′s intended destination and has denied it was ever headed for Syria.

The chief minister of Gibraltar, Fabian Picardo, said he had been assured in writing by the Iranian government that the tanker wouldn’t unload its cargo in Syria.

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The Astralship shipping agency in Gibraltar, which has been hired to handle paperwork and arrange logistics for the Adrian Darya 1, had told The Associated Press that a new crew of Indian and Ukrainian nationals had been expected to replace the sailors on board.

Messages seeking comment from the Iranian Embassy in London were not immediately returned.

Fox News' Edmund DeMarche and the Associated Press contributed to this report.