A dual national jailed in Iran has started a hunger strike in solidarity with Barry Rosen, a former hostage, who has launched a campaign at Vienna talks to draw attention to those held by Tehran.

In a tweet on Sunday, his daughter Elika saidAnoushehAshoori has joined Rosen and other hunger striking activists from his cell in Tehran's Evin prison, demanding release of all foreign hostages.

Ashoori, a British-Iranian businessman, is one of several dual nationals who are in detention in Iran on unsubstantiated charges. Ashoori has been sentenced to 10 years in prison on alleged spying for Israel.

Rosen’s hunger strike In Vienna is gathering momentum as Nizar Zakka, a Lebanese former hostage in Iran, and UK-based Iranian journalist and activist Jamshid Barzegar have also joined the sit-in.

Rosen, the former US diplomat held hostage in Iran for 444 days four decades ago, said in a tweet on Sundaythat he is feeling “very weakened but buoyed” that others are joining the campaign.

While the negotiations in Vienna are centered on reviving the 2015 nuclear agreement, the JCPOA, many have raised the issues of Iran’s human rights record and its support for militant organizations in the Middle East. There is no indication that any of these concerns are dealt with at the talks.

Iran has detained many foreigners and dual nationals who have visited the country and used them as bargaining chips against Western countries, according to human rights organizations.