When Iran seized a British-flagged tanker on Friday, it might have felt like a surprise move. But it wasn't.

It was the latest in a string of events that have led to the escalating tensions between the US, UK and Iran.

The Iranian Revolutionary Guard captured the Stena Impero and its 23 crew members in the Gulf on Friday.

Tehran says the vessel had violated international maritime rules, but the UK says it was illegally seized in Omani waters and forced to sail to the Iranian port of Bandar Abbas.

Iranian state media has released images of crew members on the vessel.

The BBC's Paul Adams explains.