The captain of an Iranian supertanker at the centre of a diplomatic standoff no longer wants to keep command of the ship, which is in need of repairs that could impede its immediate departure from Gibraltar, the sailor’s lawyer said Friday.

Any delay in the Grace 1’s departure could provide a window for the US to mount further legal action in Gibraltar seeking to seize the tanker amid a growing confrontation with Tehran.

US authorities announced in Washington late Friday afternoon that they had obtained a warrant to seize the tanker, though Gibraltar court officials said they had not received any claim by the end of the business day in the British overseas territory. It wasn’t immediately clear if the US had forwarded the warrant.

The tanker – and its 2.1 million tons of Iranian light crude oil – seemed to perform mild manoeuvres Friday but largely remained still in waters off Gibraltar a day after authorities ended its detention for allegedly breaching European Union sanctions on Syria.

The release Thursday came over the objections of the United States. The head of the Gibraltar government said Iran had promised him not to deliver the fuel to a sanctioned refinery in Syrian territory, although an Iranian official later disputed that those assurances had been delivered.

Tensions between Iran and the US have escalated since President Donald Trump last year unilaterally pulled the US out of the 2015 nuclear deal signed by Iran and other world powers.

The decision re-imposed sanctions on Iran, stopping billions of dollars in business deals, largely halting the sale of Iran’s crude oil internationally and sharply depreciating Iran’s currency, the rial. More recently, the Persian Gulf has seen attacks on oil tankers and other high-stakes confrontations.

In early July, Tehran seized the British-flagged oil tanker Stena Impero in apparent retaliation for the detention of the Grace 1. Analysts had said the release of the Grace 1 by Gibraltar could see the Stena Impero go free.

But that prospect remained up in the air Friday, with a lawyer representing three Grace 1 crew members who were released from detention Thursday casting doubt on the vessel’s immediate departure.

Richard Wilkinson told The Associated Press that the Indian national who commanded the oil tanker until it was detained in early July had asked his Iranian employers to replace him.