A British-Iranian man imprisoned in Iran is to start a hunger strike on Sunday in support of a 77-year-old American who is protesting outside nuclear talks in Vienna against Iranian hostage taking. Anoosheh Ashoori, who is being held in Evin prison in Tehran, is staging the strike in an act of solidarity with Barry Rosen, who started his own four days ago. He told the Guardian he was humbled by the support, as well as other messages being sent to him by Iranians in jail. Anoosheh, who was arrested in August 2017, has been sentenced to 10 years in jail for espionage. Rosen is protesting in Vienna outside the talks about the Iran nuclear programme, where discussions resumed earlier this month. The US has said that the longer Iran fails to comply with the 2015 Vienna accord – intended to rein in Tehran’s nuclear programme – the closer it would get to being able to build an atomic weapon. But a European Union spokesperson said on Friday an agreement was possible. Rosen and others have expressed a hope that hostages would be released as part of the deal, or alongside it. Rosen has also been joined on hunger strike by a Lebanese US resident, Nizar Zakka, who was detained by Iran between 2015 and 2019. “I am receiving heart rending messages from Iranians, and I am absolutely humbled that Anoosheh is doing this in support of me. I support him completely in return and I urge him to be careful and look after himself,” he said. Rosen, as the then US press attache to the US embassy in Tehran, was himself held hostage by Iran for 444 days between 1979 and 1981 after hard-line students stormed the embassy. Rosen admitted: “I am starting to feel tired and weak, but I am determined to continue.” He said: “I am here to call on the Americans and the Europeans to make the release of the hostages a condition of any agreement to renew the Iran nuclear deal. This has been going on for 40 years, and people are being thrown in jail with no evidence. There has to be an agreement that this will end.” He added he was struck by how ill coordinated western nations are over the hostage taking issue. “It is like herding cats. Each country seems to deal with its dual national hostages on its own. There is no sense of commonality, so they leave Iran to pick each country off. Something is missing here. The Iranians seem to be dividing and ruling. “I decided to do this two weeks ago. I am just an individual, and thought I might be a lone eagle, but it feels like a movement might be starting.” He said it was possible others would take over the hunger strike when he is unable to continue. Anoosheh’s wife, Sherry, said: “We are extremely concerned for his health as he approaches his 68th birthday, but having failed to see any progress in the Foreign Office’s efforts to secure his release and no sign of the welfare of hostages held by Iran currently being a priority of western governments, he will begin his hunger strike.”