Amnesty International has called on Iran to release eight environmentalists following what the human rights watchdog called a "grossly unfair trial" on "trumped-up" spying charges.
The London-based group issued the call in a March 5 statement, ahead of a verdict in the case expected in the coming days.
"There is evidence that they were subjected to torture and other ill-treatment including through prolonged solitary confinement in order to extract forced 'confessions'," a statement said.
The eight scientists -- all members of a local environmental group, the Persian Wildlife Heritage Foundation -- were arrested in early 2018 and went on trial in a Revolutionary Court in Tehran in January this year.
Four of the defendants were charged last year with "sowing corruption on Earth," a charge that can carry the death sentence in Iran.
Three other activists are accused of espionage and the last one has been charged with "cooperating with hostile states" against Iran and "gathering and colluding to commit crimes against national security." If convicted, they could face up to 11 years in prison.
"Protecting endangered wildlife is not a crime," said Philip Luther, Middle East and North Africa Research and Advocacy Director at Amnesty International.
"These conservationists are scientists who were carrying out legitimate research," Luther added. "It is absurd that they have been prosecuted without any evidence and are being treated as criminals."
In October, Human Rights Watch has called the accusations against the eight environmentalists "ridiculous."
The environmental activists on trial are Taher Ghadirian, Niloufar Bayani, Amirhossein Khaleghi, Houman Jokar, Sam Rajabi, Sepideh Kashani, Morad Tahbaz, and Abdolreza Kouhpayeh.
The 63-year-old managing director of the Persian Wildlife Heritage Foundation, Kavous Seyed Emami, was also detained but he died in prison under disputed circumstances.
The judiciary said the Iranian-Canadian sociology professor had committed suicide. The claim has been questioned by his family and acquaintances.