The United States says it may not issue entry visas to the crew of an Iranian tanker that has been released from detention in Gibraltar.
On Thursday, Gibraltar's Supreme Court ordered the vessel, the Grace 1, to be freed after Iran gave written assurances that it would not sail to Syria in breach of European Union sanctions.
The US State Department said it could impose the visa ban because it believes the tanker is assisting Iran's Islamic Revolutionary Guard Corps, which Washington has designated a foreign terrorist organisation.
The Grace 1 was seized by Royal Marines and local police last month.
Its detention saw Iran later seize the British-flagged oil tanker Stena Impero, which remains held by the Islamic Republic.
The Grace 1's release comes after the US under President Donald Trump pulled out of Iran's nuclear deal with world powers over a year ago, setting in motion a growing confrontation between Tehran and the West over its atomic programme.
Reacting to the latest developments, Iran's foreign minister Mohammad Javad Zarif accused the US of trying to "steal our property on the high seas".
He tweeted: "Having failed to accomplish its objectives through its #EconomicTerrorism - including depriving cancer patients of medicine - the US attempted to abuse the legal system to steal our property on the high seas," and he described the Trump administration's moves as a "piracy attempt".