Britain on Friday extended diplomatic protection to a British-Iranian mother jailed in Tehran in a move that was immediately branded by the Islamic republic as a violation of international law.
The fate of Nazanin Zaghari-Ratcliffe has been a bone of contention between Tehran and London since her arrest in Iran in January 2016.
The 41-year-old was returning from a family visit with her infant daughter when she was detained at Tehran airport.
Her husband Richard said Zaghari-Ratcliffe suffers from a range of health problems and that a lack of medical access in jail forced her to go on a brief hunger strike in protest in January.
"She's been getting very low, partly despairing.. what's the escalation beyond that?" he told AFP.
"I'm really glad that the foreign secretary has made this the escalation... It will make a difference."