An Iranian tanker at the centre of an angry confrontation between Iran and Washington sailed for Greece on Monday (Aug 20) after it was freed from detention off Gibraltar, as Washington called the release unfortunate and warned Greece and Mediterranean ports against helping the vessel, CNA reports.

Tehran said any US move to seize the vessel again would have "heavy consequences". While Iranian Foreign Minister Mohammad Javad Zarif appeared to downplay the possibility of military conflict with Washington in an interview on US television, he also indicated on a visit to Finland that Washington was seeking "more escalation".

The Grace 1, renamed the Adrian Darya 1, left anchorage off Gibraltar about 11pm (2100 GMT) on Sunday. Refinitiv ship tracking data showed on Monday that the vessel was heading to Kalamata in Greece and was scheduled to arrive next Sunday at 0000 GMT.

The seizure of the tanker by British Royal Marines near Gibraltar in Jul 4 on suspicion of carrying oil to Syria in violation of European Union sanctions led to a weeks-long confrontation between Tehran and the West. It also heightened tensions on international oil shipping routes through the Gulf.

Gibraltar, a British overseas territory, lifted the detention order on Thursday. But the next day, a federal court in Washington issued a warrant for the seizure of the tanker, the oil it carries and nearly US$1 million.

Gibraltar said on Sunday it could not comply with that request because it was bound by EU law. Washington wanted to detain the tanker on the grounds that it had links to Iran's Islamic Revolutionary Guard Corps (IRGC), which it has designated a terrorist organisation.