The new UK foreign secretary, Liz Truss, will on Monday call for the immediate and permanent release of all British detainees held in Iran when she meets the Iranian foreign minister, Hossein Amir-Abdollahian, in New York. Nazanin Zaghari-Ratcliffe, the most prominent of the dual nationals, will mark her 2,000th day detained in Iran on Thursday and her supporters have called for the Foreign Office to step up pressure on Iran by imposing sanctions on 10 officials seen as implicated in state hostage-taking since 1979. The 10 Iranians – lawyers, jailers and propagandists – would be subject to UK travel bans and asset freezes. Speaking on the eve of her meeting, the first between Iran and the UK at foreign minister level since 2018, Truss said she would urge her Iranian counterpart to “ensure the immediate and permanent release of all arbitrarily detained British nationals in Iran, and to begin working with us to mend our fractured relations”. Sources told the Guardian on Sunday that a complex multi-state deal to secure the release of at least three British detainees fell apart earlier this year over the terms of the release of some US detainees. The deal would have apparently involved the transfer of £400m to Iran via a Swiss bank account to cover a longstanding and acknowledged debt dating back to the Iranian revolution. Britain has always insisted that the release of the British detainees, mainly dual nationals, could not be linked to payment of the debt. Truss also warned that the continued delays in the return of the new government to the talks in Vienna on the revised nuclear deal “means less space for diplomacy”. The new hardline government in Tehran is still deciding the makeup of a negotiating team and its revised demands. The Iranians are likely to seek fresh guarantees about what would happen if the US returned to the deal and lifted sanctions, but then a future administration followed Donald Trump’s example and pulled out again. They want guarantees that the Europeans would be able to find a way to sidestep US sanctions and keep trading with Iran. Iran want Russia and China to be allowed to use the EU’s financial mechanism designed to avoid US sanctions. Zaghari-Ratcliffe was arrested in April 2016 and is refused permission to leave Tehran even though she has completed her initial five-year sentence. A dossier naming the 10 Iranians who could be sanctioned is being sent to Truss by the Free Nazanin campaign and Redress, the legal advisers who have sought her release. They say they will submit two further lists of Iranian officials in the months ahead, and that the list was compiled through talking to 25 families who have been subject to arrest, jailing and being used as a negotiating lever. Richard Ratcliffe, the husband of Zaghari-Ratcliffe, said: “Iran conducts its diplomatic business through hostage-taking, in part because it is cost-free. “British citizens will not be protected from hostage-taking by words and soundbites, but by actions that cause the perpetrators to reassess their calculations, and consider the personal costs – for their role in what is a serial organised crime.” He added: “Diplomacy is not an abstract science; it has to be personal. This means the foreign secretary needs to be proactive when she engages with Iran this coming week, and she needs to be brave. Or there will be more hostages taken by Iran, and new copycat regimes.” Truss is the fifth UK foreign secretary to be handed the Zaghari-Ratcliffe file, and many of them have promised to leave no stone unturned, but none so far has been willing to describe her arrest, sentencing and detention as state hostage-taking. Redress claims her case is one of at least 30 of foreign nationals who have been arbitrarily detained in Iran for diplomatic leverage in recent years. The 10 Iranians who would be subject to sanction are said to have been involved in various stages of her detention, ranging from initial arrest and interrogation, the legal proceedings, abuse in prison amounting to torture, false propaganda, and her deployment as an asset in diplomatic negotiations. For security reasons the campaign is not releasing the names of the 10 at this stage. Redress claims Iran’s practice of arbitrarily detaining, torturing and mistreating foreign and dual nationals for diplomatic leverage over other states amounts to state hostage-taking, both in fact and in law. It adds that Iran’s state hostage-taking practice constitutes “sanctionable activities” under the UK’s global human rights sanctions regime and its Iran sanctions human rights regime. Some of the perpetrators identified have already been sanctioned. The campaign is in part an effort to persuade governments, not just in the UK, to recognise that they are dealing with a systematic practice that needs identifying before it can be stamped out. At various times UK foreign secretaries have agreed that Zaghari-Ratcliffe is a hostage, but generally they have been reluctant to say as much in public. Since her arrest in April 2016, Zaghari-Ratcliffe has spent more than eight months in solitary confinement and been denied urgent medical treatment. She was released from house arrest on 7 March this year but was immediately retried on a second set of charges on 14 March. She was sentenced to a further one-year jail sentence and one-year travel ban on 26 April. This sentence has not yet been implemented pending the outcome of an appeal, as yet unscheduled.