Jeremy Hunt has visited Iran to make a personal appeal for the immediate release of the Iranian-British dual-national Nazanin Zaghari-Ratcliffe on humanitarian grounds.

The foreign secretary is also call on Iran to stop using Zaghari-Ratcliffe and other dual nationals as tools of diplomatic leverage.

Zaghari-Ratcliffe was arrested in April 2016 as she and her daughter were about to board a flight back to the UK after a visit to her family in Iran. She was found guilty of spying and given a five-year jail sentence. She denies the allegations, and her plight has left a shadow hanging over Iran-UK relations.

In August, she was granted a three-day release from Evin prison but her request for an extension was denied and she was forced to say goodbye to her four-year-old daughter, Gabriella, and return to jail, where she had a panic attack. Her family have decided not to apply for further temporary releases because of the tremendous strain she has suffered.

Profile Who is Nazanin Zaghari-Ratcliffe? Show Nazanin Zaghari-Ratcliffe is an Iranian-British dual national who has been jailed in Iran since April 2016. She has been accused of attempting to orchestrate a “soft overthrow” of the Islamic Republic. She and her three-year-old daughter, Gabriella, were about to return to the UK from Iran after a family visit when she was arrested. Since then, she has spent most of her time in Evin prison in Tehran, separated from her daughter. In January 2019 she went on hunger strike for three days in protest against being denied medical care in Tehran’s Evin prison. In March, the UK Foreign Office granted her diplomatic protection, a step that raised her case from a consular matter to the level of a dispute between the two states. Zaghari-Ratcliffe worked for BBC Media Action between February 2009 and October 2010 before moving to Thomson Reuters Foundation, the news agency’s charitable arm, as a project manager. Her family has always said that she was in Iran on holiday. Photograph: Nazanin Zaghari-Ratcliffe/PA

“More than anything, we must see those innocent British-Iranian dual-nationals imprisoned in Iran returned to their families in Britain,” Hunt said before a meeting with the Iranian foreign minister, Mohammad Javad Zarif. “I arrive in Iran with a clear message for the country’s leaders: putting innocent people in prison cannot and must not be used as a tool of diplomatic leverage.”

Hunt has twice met Zaghari-Ratcliffe’s husband, Richard, promising him that he would leave no stone unturned in order to secure her release.

There had been hopes that Hunt’s takeover of the Foreign Office from Boris Johnson in August, coupled with the British decision to stick with the Iran nuclear deal in the face of sustained US pressure, might prompt Tehran to release Zaghari-Ratcliffe on compassionate grounds.

Although the foreign secretary is due to press the Iranian foreign ministry hard on dual-national cases, there is a good deal of realism about the possibility of an immediate breakthrough. The foreign ministry is not seen as the key decision maker, so Hunt would ideally like to meet members of the judiciary, who hold greater sway.

Hunt’s visit is the first by a European foreign minister since the US pulled out of the deal, although Zarif has met EU ministers in Vienna to urge Europe to do more to protect European firms still seeking to trade with Iran from the effect of American sanctions.

The US pulled out of the deal signed by Barack Obama in 2015, saying it was full of holes, and announced it would impose sanctions, including fines and asset freezes, on the US arm of any European company seeking to continue to trade with Iran.

Brian Hook, the US special representative for Iran, last week expressed confidence that almost no European firms were willing to risk US sanctions. A succession of companies have pulled out of planned investments in Iran, leaving some medium-sized organisations with no US operations to assess the risk of continuing to trade.

The British decision to side with France and Germany has caused a rift with Washington. Theresa May was reportedly rebuked by Donald Trump in a bad-tempered phone call, initiated by May to congratulate the US president for the midterm election results. The final tranche of US sanctions on Iran, including sanctions on any country importing Iranian oil, came into force on 5 November.

The UK – unlike the US – believes the economic pressure being applied by the US on Iran will not force the country to reopen the deal, and – if anything – will strengthen Iranian hardliners.

Some leading Republicans are convinced that the Iranian regime is close to collapse, and Hunt’s visit will be a brief chance to test that assessment.

Hunt will stress that the UK remains committed to the nuclear deal as long as Iran sticks to its terms, and will discuss European efforts to maintain nuclear-related sanctions relief. The UK has said that because of Brexit it cannot host the EU’s proposed special purpose vehicle, a device that could enable companies to continue to trade with Iran but avoid US sanctions. It is not clear if any country is willing to risk sanctions by hosting the SPV, a serious blow to Europe’s efforts to show its independence from US foreign policy.

Hunt said: “The Iran nuclear deal remains a vital component of stability in the Middle East by eliminating the threat of a nuclearised Iran. It needs 100% compliance, though, to survive. We will stick to our side of the bargain as long as Iran does.”

Hunt will also discuss Yemen, and underline his concern at reports, documented by the UN panel of experts, that Iran has supplied ballistic missiles and weapons to the Houthis, in violation of security council resolutions. The UK will table a draft resolution at the UN security council on Monday setting out the plans for a ceasefire leading to talks.

Speaking during a tour of Tehran’s Grand Bazaar on Monday morning, Hunt said: “This is part of the world that is quite frankly a tinderbox. We want to move to peace in Yemen – that is our number one priority at the moment. We also have the case of Nazanin Zaghari-Ratcliffe and other dual nationals who are in prison who should not be. We want to get them home, so all these things have to be discussed.”