BEIRUT, Aug 27: Having struck a historic nuclear deal to end decades of enmity between Iran and the West, President Hassan Rouhani faces a fresh challenge at home, to win the release of leading political prisoners whose case has polarized the Islamic Republic. Former presidential candidates Mir Hussein Moussavi and Mehdi Karroubi, along with Moussavi’s wife Zahra Rahnavard, have been under house arrest since 2011. Securing the release of the high profile trio would fulfill one of Rouhani’s biggest campaign promises two years ago, but it is fraught with risks and could lead to an outright showdown with Iranian hardliners, experts say. Just how important the issue is to Rouhani’s supporters was made clear after the announcement of the nuclear deal last month, when people celebrating in the streets of Tehran held up pictures of Moussavi and Karroubi and chanted for their release. The two men, who both ran against Mahmoud Ahmadinejad for Iran’s presidency in the disputed 2009 elections, came to be seen as figureheads of the country’s reformist “green movement”.