Iran has warned the United States against attempting to seize the Grace 1 oil tanker on the high seas after it departed from Gibraltar following a six-week crisis.
The Grace 1, which was renamed the Adrian Darya 1 over the weekend, left an anchorage off Gibraltar after dark on Sunday night after a court dismissed an attempt by the United States to have it impounded.
This morning ship tracking data showed it heading slowly east, bound for the port of Kalamata in Greece.
Asked about the possibility of the US seizing the vessel by force at sea, Abbas Mousavi, an Iranian foreign ministry spokesman, said: "Such an action, and even the talk of it...would endanger shipping safety in open seas
"Iran has issued the necessary warnings through official channels, especially the Swiss embassy, to American officials not to commit such an error because it would have heavy consequences," he told Iranian television.
A Royal Marine boarding party seized the Grace 1 after it sailed into Gibraltar's waters on July 4, sparking a weeks long standoff between Tehran and London that culminated in Iran seizing a British flagged tanker, the Stena Impero, in the Persian Gulf.
The governments and Britain and Gibraltar said they suspected the vessel of carrying oil to Syria, in breach of sanctions against Bashar Assad's regime.
Iran accused Britain of acting on behalf of the United States, which has tried to blockade Iranian oil exports as part of a "maximum pressure" policy against Tehran, and sent revolutionary corps gunboats to seize the Stena Impero, a British flagged tanker, in the gulf on July 19.
However, Mr Mousavi on Monday denied the Stena Impero had been taken in a tit-for-tat action and said it would only be released after an Iranian court had reviewed "violations" it had committed.
Heshmatollah Falahatpisheh, a member of the Iranian parliament's national security and foreign affairs committee, appeared to hint that the British tanker would be held for several more days or even weeks.
"Until the Iranian oil tanker arrives at its destination the British must help end the crisis," Mr Falahatpisheh was quoted as saying by the semi-official ISNA news agency.
"This means that the crisis with Britain is not over. Britain has the primary responsibility for ending the oil tanker crisis," he said.
A Gibraltar court cleared the Grace 1 to proceed last week after assurances were provided that it would not sail to Syria.
The United States then applied or the vessel to be impounded on the grounds that its cargo is controlled by the Iranian Revolutionary Guard Corps, which the US designates a terrorist organisation. The court rejected the application because Gibraltar is not within US jurisdiction.