An Iranian ship held by Gibraltar since July on suspicion of transporting oil to Syria has left port.
Marine tracking shows the tanker moving east into the Mediterranean and lists Kalamata in Greece as the destination.
Gibraltar earlier rejected a request by the US to again seize the ship, which has changed its name from Grace 1 to Adrian Darya-1.
The US made the last-minute request on Friday, a day after Gibraltar lifted its detention order.
Gibraltar said it could not comply with Washington’s request to issue a new detention order because US sanctions against Iran did not apply in the EU.
Tehran said it was ready to dispatch a naval escort to the Adrian Darya-1.
A British-flagged tanker seized in July remains in Iranian hands. There had been speculation of a swap if Grace 1 was freed, despite official denials.
A spokesman for the Iranian foreign ministry said on Monday they were waiting for a court order before any possible release of the ship but said there was “no connection whatsoever” between the two ship seizures.
He also warned the US not to attempt to seize the ship in international waters. On Friday, the US issued a warrant for the tanker’s seizure, following Gibraltar’s refusal to comply with Washington’s request.