An Iranian tanker at the center of an angry confrontation between Iran and Washington sailed for Greece on Monday after it was freed from detention off Gibraltar, as Washington called the release unfortunate and warned Greece and Mediterranean ports against helping the vessel.

A U.S. court has issued a warrant for the seizure of an Iranian tanker that British Royal Marines had seized last month in Gibraltar, a court document showed on Friday.

Gibraltar's Supreme Court on Thursday ruled in favour of releasing an Iranian supertanker seized on suspicion of shipping oil to war-torn Syria in breach of international sanctions, in a blow to the United States which had tried to block the vessel's departure.

The British territory of Gibraltar will on Thursday release an Iranian oil tanker seized by Royal Marines in the Mediterranean in July, the Sun newspaper reported, citing sources close to Gibraltar Chief Minister Fabian Picardo.

A highly placed Gibraltarian government source denied on Tuesday an Iranian news agency report which said the Iranian oil tanker Grace 1 would be leaving the British overseas territory on Tuesday.

Gibraltar police said on Friday that all four crew members of the Iranian Grace 1 tanker have been released on bail without charge after it was detained last week on suspicion of breaking European sanctions by taking oil to Syria.

Gibraltar police said they have arrested the captain and chief officer of the detained Iranian Grace 1 supertanker accused of violating EU sanctions on Syria and have seized documents and electronic devices from the vessel.