Nazanin Zaghari-Ratcliffe will appear in an Iranian court on Sunday after the country’s state media said she faced a new and unspecified charge. The news came as a bombshell to the family of the British-Iranian dual national, who has been under effective house arrest ever since the coronavirus outbreak led to her release from prison after serving nearly four of her of her five-year sentence. The new charges against Zaghari-Ratcliffe, confirmed to her British MP, Tulip Siddiq, have not yet been revealed. She was informed of them when she appeared before a branch of the country’s revolutionary court in Tehran on Tuesday, where she was first sentenced in 2017. Her current charges expire in roughly six months. “I know many people are concerned about her welfare and I’ll keep everyone updated when we have more information,” Siddiq said. The UK Foreign Office condemned the news: “Iran bringing new charges against Nazanin Zaghari-Ratcliffe is indefensible and unacceptable. We have been consistently clear that she must not be returned to prison.” Since her release from Tehran’s notorious Evin prison she has been wearing an ankle tag that limits her movements to within 300 metres (984ft) of her parent’s home in Tehran. She had been hoping to be reprieved of the final year of her sentence on the basis that she qualified for an amnesty under general terms set out by the Iranian supreme leader, Ayatollah Ali Khamenei. The news was a bitter blow to her daughter – who was brought back to the UK last year – and husband Richard in London, even though the possibility of being charged with further offences had never disappeared. Zaghari-Ratcliffe was arrested during a holiday with her daughter Gabriella, now six, in April 2016. Her family says she was in the country to visit family, and denies accusations she was plotting the “soft toppling” of Iran’s government. Zaghari-Ratcliffe worked for the Thomson Reuters Foundation, the charitable arm of the news agency. The new charges came after the UK defence secretary, Ben Wallace, in a letter to the family said the British government did owe the Iranian government an outstanding debt on a payment the late Iranian shah Mohammad Reza Pahlavi made for Chieftain tanks that were never delivered. He had said the government was looking at every legal avenue to pay the debt, thought to be as much as £400m. The shah abandoned the throne in 1979 and the Islamic revolution soon installed the clerically overseen system that endures today. The UK says the debt issue, which Wallace for the first time formally acknowledged the government owes, runs parallel with the detention of dual nations by Iran. Iranian officials had responded to the Wallace letter by saying her detention was nothing to do with the debt issue. The fresh charges may be an attempt by hardliners to underscore this point, or to gain further leverage over the UK government. Different factions within the Iranian government take a different approach to the use of political prisoners and the Islamic Revolutionary Guards are the most hardline about the need to detain security prisoners. The shadow foreign secretary, Lisa Nandy, has urged the UK to develop a cross-government strategy to secure Zaghari-Ratcliffe’s release, but the foreign secretary, Dominic Raab, said he had raised her case repeatedly with Iranian officials including the foreign minister Javad Zarif. The former foreign secretary Jeremy Hunt said: “Nazanin has already served most of her sentence for a crime she didn’t commit. This is hostage diplomacy and Iran needs to know that Britain will not stand for it.” The shadow foreign secretary, Lisa Nandy, said the news was deeply concerning, adding: “The UK government must take every possible step to get her home safely.” Kate Allen, Amnesty International director, said: “As a matter of absolute urgency the UK government should make fresh representations on Nazanin’s behalf, seeking to have any suggestion of a second trial removed.” The Foreign Office had already been alerted to reports in the Iranian press that a potential appointment to the UK embassy in Tehran as commercial attache was being challenged on the basis that she might be a spy. The accusation has been levelled against Margot Arthur who has an Iranian grandmother and can speak Persian. The new charges against Zaghari-Ratcliffe come as tensions escalate between European powers and Iran over the future of its nuclear deal. Britain is coming under special pressure from the US to agree to the snapback of all UN sanctions and to continue the UN conventional arms embargo on Iran rather than to allow it to expire in October. At present the US is isolated at the UN amongst the big powers in saying it can impose a snapback, but the UK is seen by the US as more likely than France and Germany to succumb to American pressure. Hopes were raised in March that Zaghari-Ratcliffe would soon return home to Britain when she was granted temporary release from prison as a result of the coronavirus pandemic. She was however the only prisoner granted furlough during that period forced to wear an ankle tag limiting her movements, which her husband said at the time meant her release was much closer to a house arrest than it was to regular furlough. Iran has been hit hard by the virus, becoming the worst-affected country in the Middle East with more than 391,000 cases and 22,542 deaths. Tens of thousands of inmates, including large numbers of political prisoners, were released as Iran tried to curb the spread of the virus in its crowded prisons. Iran on Tuesday confirmed the death sentence of wrestling champion Navid Afkari for participating in 2018 protests against the regime. It is also seeking to deport from Turkey an Iranian women’s rights activist Maryam Shariatmadari sought by Iran for involvement in a protest about the compulsory wearing of the hijab. She was arrested by Turkish police on Monday night, but has since been released.