Human rights groups have called for an independent investigation into the death of Kavous Seyed Emami, a top environmentalist and academic, who died in mysterious circumstances while in detention at Tehran's Evin Prison.

Hadi Ghaemi, executive director of the Center for Human Rights in Iran (CHRI), said on Monday that the prosecutor's report claiming Seyed Emami committed suicide has "no credibility whatsoever.

"This is a prison system out of control and a judiciary that is actively colluding in a massive cover-up," Ghaemi, who is based in New York, said.

He said the judiciary must also allow "an independent and transparent autopsy" in order for his family and the public to know how he died.

Seyed Emami was one of the founders of the Persian Wildlife Heritage Foundation, which is working to protect Iran's wildlife and promote conservation projects.

Yasamin Alttahir, Middle East and North Africa spokesman at Amnesty International, told Al Jazeera on Monday that the rights group too supports an independent investigation on Seyed Emami's death.

Alttahir said that in the section of Evin Prison where the environmentalist was apparently kept, detainees are stripped of all their possessions, making the suicide claim even "more suspicious".

On Saturday, Seyed Emami's son announced on social media the death of his father.

"The news of my father's passing is impossible to fathom," Ramin Seyed Emami, a popular singer, wrote on Instagram, with a photo of himself as a child playing with his father.

"Kavous Seyed Emami was arrested on Wednesday 24 January 2018, and the news of his death was released to my mom, Maryam, on Friday the 9th of February. They say he committed suicide. I still can't believe this."

Seyed Emami's death was the third case labelled by authorities as a suicide in recent weeks inside Evin.

'Shocked and saddened'

Erik Solheim, head of the United Nations Environment Programme, said on Monday that he is "shocked and saddened" by the news of Seyed Emami's death.

"Also very concerned by a number of arrests of environment figures," he wrote on social media.

Gary Lewis, a UN official formerly based in Tehran, also paid tribute to Seyed Emami, calling him "a good man who loved nature and Iran.

"He was my friend and he will be missed".

On Sunday, Abbas Jafari-Dolatabadi, Tehran's prosecutor general, said the environmentalist "was accused of espionage and committed suicide after confessing his crimes while in prison".

He also said that a hunter-businessman named Morad Tahbaz was also arrested.

Tahbaz, who is a member of the Strategic Committee for Protecting Iranian Cheetah, is a dual Iranian and American citizen.

In another development, Kaveh Madani, the deputy of Iran's environment department, was reportedly imprisoned, according to Mahmoud Sadeghi, a parliament member allied with President Hassan Rouhani.

However, in a post on Monday afternoon, Iran's environment department posted an undated photo of Madani alongside Isa Kalantari, Iran's environment minister, holding a meeting with Michael Klor-Berchtold, Germany's ambassador to Iran, at the environment ministry offices in Tehran.

Meanwhile, Ghaemi, of the Center for Human Rights in Iran, has urged the Canadian government to "take the lead in calling for an international investigation" into the death of Seyed Emami, who is a dual citizen of Iran and Canada.

He said it is a "big test" for Prime Minister Justin Trudeau's foreign policy.

Omid Memarian, a US-based Iranian journalist once imprisoned in his home country, called Seyed Emami's death "Cover-up 101", and called on President Hassan Rouhani and Javad Zarif, the foreign minister, to take action.

"You have constantly urged dual nationals to go back to Iran and serve their homeland. Now that Iranian-Canadian Kavous Seyed Emami has died suspiciously in custody, the family has the right to order an autopsy. Do your job and defend their rights!" Memarian wrote on Twitter.

As of Monday morning, Seyed Emami's remains had not been given to his family.

The Center for Human Rights in Iran said the judiciary has told Seyed Emami's family they would receive his body on Tuesday morning "on the condition that they immediately and quietly bury him".

In response to questions by the Iranian Labour News Agency, judiciary spokesman Gholam Hossein Mohseni Ejeie said he "heard" of the suicide claim.

"But I don't know the details. The investigation is under way to see how it happened."