The Iranian Grace 1 oil tanker on Sunday night left the waters of Gibraltar, more than a month after being seized by British authorities, media in Gibraltar reported.
The trail left by GPS data on Marinetraffic.com, a vessel tracking service, showed the Iran-flagged tanker, which earlier on Sunday changed its name to Adrian Darya 1, moving shortly before midnight.
The tanker slowly steered Southeast toward a narrow stretch of international waters separating Morocco and the southern tip of the Iberian Peninsula, according to The Associated Press.
The UK and Gibraltar seized the Iran-flagged tanker Grace 1 in early July on the grounds that it was attempting to transport oil to Syria, a violation of EU sanctions.
Iran later seized the British-flagged Stena Impero in the Persian Gulf. However, Iranian Foreign Minister Mohammad Javad Zarif denied the move was an act of revenge for the capture of the Iranian tanker, claiming Iran had taken measures against the ship to implement international law.
The ship left Gibraltar hours after local authorities rejected an eleventh-hour attempt by the United States to recapture the oil tanker.
Gibraltar's government said earlier on 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."