LONDON (Reuters) - The wife of an Iranian-Canadian environmental activist who died in prison in Tehran last month was barred from leaving Iran, one of her sons said, in an unexplained move that drew an angry response from Canada.

Raam Emami said in an email to journalists that security forces had not allowed his mother, Maryam Mombeini, to get on a plane to Vancouver with him and his brother on Wednesday night.

Mombeini is the widow of Kavous Seyed-Emami, an environmental activist and sociology professor who was arrested on Jan. 24 and died in prison. Iran’s judiciary said Seyed-Emami, 63, had committed suicide.

The family has called for an independent investigation of his death.

Canada’s Minister of Foreign Affairs, Chrystia Freeland, said in a message posted on Twitter that she was “outraged” to learn that Mombeini had been barred from leaving Iran.

“We demand that, as a Canadian, she be given the freedom to return home,” she added.

Iranian judiciary officials were not immediately available for comment.

Seyed-Emami was the managing director of the Persian Wildlife Heritage Foundation, which seeks to protect Iran’s rare animals. Iran’s judiciary said he had set up the NGO as a cover to collect classified information on Iran’s missile program.

Raam Emami said the family decided to leave Iran after being constantly “harassed”.

“The government raided our home and seized all of our valuables (most importantly deeds to our homes),” he said. “We can no longer stand this state of constant terror.”

Raam Emami has previously said that the family was under pressure from authorities not to publicize the case of Seyed-Emami.

“The authorities told our lawyers to tell the brothers ‘to shut up or we’ll shut them up,’ Emami said, adding government agents had told him they were watching him.

Human rights activists have reported that at least six detainees have died in prison in the last two months in Iran. The judiciary has confirmed three deaths in custody but said all three had committed suicide.

President Hassan Rouhani last month appointed a committee to investigate the incidents in prisons.

Shahindokht Molaverdi, Rouhani’s special assistant on civil rights and a member of the committee, said on Thursday that Rouhani was “serious about investigating” the death of Seyed-Emami and other prisoners.

She said the committee has met families of some deceased prisoners.

Bilateral ties between Iran and Canada worsened in 2003 when an Iranian-Canadian photojournalist, Zahra Kazemi, died in Tehran’s Evin prison while in custody.

Canada cut all diplomatic ties with Iran in 2012.