The US justice department has issued a warrant to seize a detained Iranian oil tanker, a day after a judge in Gibraltar ordered it to be released.
The Grace 1 supertanker, which is carrying 2.1m barrels of oil, was detained on 4 July on suspicion of illegally transporting oil to Syria.
A last-minute legal attempt by the US to keep the tanker detained was rejected by Gibraltar on Thursday.
Iran previously called the detention of Grace 1 an "illegal interception".
Two weeks after Grace 1 was detained, on 19 July, Iran seized the British flagged tanker Stena Impero in the Strait of Hormuz.
Although Iran claimed the ship had violated "international maritime rules", the seizure of Stena Impero was widely believed to be an act of retaliation.
What is the US saying?
The warrant, issued by a US federal court in Washington on Friday, is addressed to "the United States Marshals Service and/or any other duly authorized law enforcement officer".
It called for the tanker and the oil on board to be seized. It has also ordered the seizure of $995,000 (£818,000) from an account at an unnamed US bank linked to Paradise Global Trading LLC, an Iranian company.
The justice department said the ship and the firm had been involved in violations of the International Emergency Economic Powers Act, bank fraud, money laundering and terrorism forfeiture statutes.
"A network of front companies allegedly laundered millions of dollars in support of such shipments," federal prosecutor Jessie Liu said.
She added the parties involved were linked with Iran's Islamic Revolutionary Guard Corps, which the US regards as a foreign terrorist organisation.
Although the warrant orders "any" law enforcement officer to seize the tanker and its cargo, it is unlikely to result in any action by the UK or Gibraltarian authorities, according to Prof Fawaz Gerges, a professor of Middle Eastern politics and international relations at LSE.
He said: "It would take a great deal of arm-twisting [by the US] to really persuade another Gibraltarian court to take the tanker back."
What happened in Gibraltar?
Gibraltar's government said it had received assurances from Iran that Grace 1 would not sail to countries "subject to European Union sanctions" - that is, Syria.
The British territory's chief minister Fabian Picardo added: "We have deprived the Assad regime in Syria of more than $140m worth of crude oil."
After a judge ordered the tanker's release, Mr Picardo earlier told the BBC that the vessel would be able to leave as soon as the logistics had been figured out: "Could be today, could be tomorrow."
Neither Britain nor Gibraltar have responded to the US warrant.