The United States is reportedly beginning efforts to seize an Iranian supertanker suspected of violating EU sanctions on oil shipments to Syria.
Tanker Grace 1, carrying Iranian oil, was seized last month in a British Royal Navy operation off Gibraltar.
The US Justice Department has made a last-minute application to extend the ship's detention, which will be consiered by Gibraltar's attorney general.
Gibraltar said the application contains a "number of allegations which are now being considered".
It is the latest development in an escalating international tit-for-tat over oil tankers in the Persian Gulf.
Gibraltar dropped legal proceedings against the crew of the tanker, which has been detained since July 4, as part of efforts to "de-escalate" the situation.
The seizure of the tanker in July sparked tensions between the UK and Iran, leading to British-flagged and Swedish-owned tanker Stena Impero being seized by Iran in the Gulf.
