Britain is weighing its next moves in the Gulf tanker crisis, with few good options apparent as a recording emerged showing the Iranian military defied a British warship when it boarded and seized a ship three days ago.
Prime Minister Theresa May's office says she will chair a meeting of Britain's COBR emergency response committee in London on Monday morning to discuss the crisis.
Little clue has been given by Britain on how it plans to respond after Iranian Revolutionary Guards rappelled from helicopters and seized the Stena Impero in the Strait of Hormuz on Friday in apparent retaliation for the British capture of an Iranian tanker two weeks earlier.
Footage obtained by Reuters from an Iranian news agency on Sunday showed the tanker docked in an Iranian port with Iran's flag hoisted atop.
The British government is expected to announce its next steps in a speech to parliament on Monday but experts on the region say there are few obvious steps London can take at a time when the United States has already imposed the maximum possible economic sanctions, banning all Iranian oil exports worldwide.
"We rant and rave and we shout at the ambassador and we hope it all goes away," said Tim Ripley, a British defence expert who writes about the Gulf for Jane's Defence Weekly.
"I don't see at this point in time us being able to offer a concession that can resolve the crisis. Providing security and escort for future ships is a different matter."
A day after calling the Iranian action a "hostile act", top British officials kept comparatively quiet on Sunday, making clear that they had yet to settle on a response.
"We are going to be looking at a series of options," junior defence minister Tobias Ellwood told Sky News.
"Our first and most important responsibility is to make sure we get a solution to the issue to do with the current ship, make sure other British-flagged ships are safe to operate in these waters and then look at the wider picture."
The Iranian capture of the ship in the global oil trade's most important waterway was the latest escalation in three months of spiralling confrontation with the West that began when new, tighter US sanctions took effect at the start of May.
Washington imposed the sanctions after President Donald Trump pulled out of a deal signed by his predecessor Barack Obama, which had provided Iran access to world trade in return for curbs on its nuclear program.
European countries including Britain have been caught in the middle. They disagreed with the US decision to quit the nuclear deal but have so far failed to offer Iran another way to receive the deal's promised economic benefits.
Britain was thrust more directly into the confrontation on July 4, when its Royal Marines seized an Iranian tanker off the coast of Gibraltar, with Britain accusing it of violating sanctions on Syria.
While Iran's official line is its capture of the Stena Impero was because of safety issues, it has done little to hide that the move was retaliatory.
The tactics it used - with masked troops rappelling from helicopters - matched those the British had used two weeks before.
Iran's Foreign Minister, Mohammad Javad Zarif, blamed Washington and Trump's hawkish national security adviser John Bolton for luring Britain into conflict.
"Having failed to lure @realDonaldTrump into War of the Century ... @AmbJohnBolton is turning his venom against the UK in hopes of dragging it into a quagmire," Zarif wrote on Twitter.
"Only prudence and foresight can thwart such ploys."