A Navy veteran from California seized in Iran a year ago has yet to speak with his mother. A British-Iranian woman held in a Tehran prison since 2016 has been moved to a hospital psychiatric unit, incommunicado with her family. A French-Iranian scholar has been arrested without explanation while visiting Iran, just as France is exerting diplomacy to help save the nuclear agreement.

Each case is different, but all share the backdrop of an escalating confrontation between Iran and the United States, and fury among hard-line Iranian conservatives over what they see as Europe’s subservience to America.

The United States has long contended, since the Tehran hostage crisis four decades ago, that the Iranians use foreign prisoners as pawns for political leverage. Rights advocates say the prisoners are plunged into a judicial system that is mysterious and arbitrary.