Boris Johnson to flag case of imprisoned British-Iranian mother at summit
The EU met on Thursday to discuss the nuclear deal with Iran following American president Donald Trump's threat to reimpose sanctions on Tehran.
Trump has repeatedly criticised the deal and refused in October to confirm that Iran was complying with it.
"The deal is working, it is delivering on its main goal which means keeping the Iranian nuclear programme in check," vice-president of the EU commission Federica Mogherini said, stressing the importance of preserving an agreement she said is "making the world safer and... preventing a potential nuclear arms race in the region".
Johnson is set to discuss the case of Nazanin Zaghari-Ratcliffe with Mohammad Javad Zarif as the pair meet for the second time in two months. Johnson visited Tehran earlier this month to press for her release on humanitarian grounds.
Zaghari-Ratcliffe, who works for the Thomson Reuters Foundation, is serving five years for taking part in mass protests in 2009, which she denies.
She was arrested at Tehran airport on April 3, 2016, after visiting relatives with her young daughter.
While there had been hopes for an early release after Zaghari-Ratcliffe's husband was informed by the Iranian lawyer that she had been "marked for early release" following an update on Iran's judicial database, they were quickly crushed.
The case has become highly politicised, especially after a careless blunder by Johnson last month in which he stated that Zaghari-Ratcliffe had been training journalists in Iran - something the Thomson Reuters Foundation and her family have strongly denied. This has been used by the Iranian authorities to help justify the new charges and may contribute to her potentially lengthened sentence.
"The government remains very concerned about all our dual nationals detained in Iran and has been doing everything it can to make progress on their cases, while approaching them in a way that we judge is in their best interests," a Foreign Office spokesman said.
An online petition for her release has collected almost 1.5 million signatures.