An Iranian official said Tuesday the country has no plans to swap three American prisoners for a missing nuclear scientist who Tehran claims was abducted by the US. Foreign Ministry spokesman Ramin Mehmanparast said it's not Iran's practice to “exchange people whose cases are still with the judiciary” and dismissed suggestions that the fate of the three Americans is linked to that of scientist Shahram Amiri. “These two cases are not comparable,” Mehmanparst told reporters in Tehran. “Iran will use legal channels to secure the release of Amiri.” Iran claims the scientist was abducted by the US in 2009. The three Americans – Sarah Shourd, her boyfriend, Shane Bauer of Minnesota, and their friend Josh Fattal – were arrested along the Iraqi border last July. Iran has accused them of espionage and entering the country illegally. Their families say the three were hiking in Iraq's largely peaceful mountainous northern Kurdish region and that if they crossed the border, it was accidental. Iran allowed the mothers of the three to visit them in May, the families' first contact with them since they were taken into Iranian custody. The mothers had hoped to secure their children's' release, but returned empty-handed to the United States after a two-day visit. Also in May, Iran's intelligence minister Heidar Moslehi signaled Tehran might be open to a prisoner swap with the US for the three Americans. President Mahmoud Ahmadinejad had also mentioned a swap in March, but nothing was officially proposed. Before Amiri disappeared, he worked at Iran's Malek Ashtar University, an institution closely connected to the country's powerful Revolutionary Guard.