Five environmentalists have been charged in Iran with national security crimes punishable by death, in a development the UN environment head said was deeply troubling.

The activists from the Persian Wildlife Heritage Foundation were arrested in January alongside at least four other people, and face allegations of spying, which human rights campaigners and Iran’s own government say are unfounded.

Concerns about environmental challenges, including water shortages, were a trigger for nationwide protests that began early this year before taking on a wider political dimension. They came as Iran faces its worst drought in modern times.

The impasse has undermined the administration of Hassan Rouhani, which has remained adamant that there is…