The federal government is being urged to allow torture victims to sue foreign states in Canadian courts, after a Montreal man lost a long battle to sue Iran over the beating death of his mother.

The Supreme Court ruled 6-1 on Friday that current federal law does not allow Stephan Hashemi to sue Iran in Canadian courts for the 2003 torture, sexual assault and death of Zahra Kazemi, an Iranian-Canadian photojournalist who had been covering protests outside Evin Prison, near Tehran.

But the court made it clear that the principle of state immunity from lawsuits in foreign courts can give way if Parliament decides it should. It already has in cases where a foreign state has supported terrorism. The Conservative government created that exception in 2012, allowing lawsuits over terrorist acts committed since 1985.

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"There's an important message in the ruling – Parliament has to do something about this," Mathieu Bouchard, a Montreal lawyer who represented Mr. Hashemi, said in an interview. "There should be an exception for all gross violations of human rights."

Clarissa Lamb, a spokeswoman for Justice Minister Peter MacKay, would say only that the government is reviewing the court's decision.

In creating the terrorism exception, Ottawa rejected attempts to add torture or genocide, and a private member's bill to do so sponsored by former Liberal justice minister Irwin Cotler did not become law. The United States allows torture lawsuits against foreign governments, but only those that are on a government list of state sponsors of terrorism – a list that includes Iran.

Justice Louis LeBel, writing for the majority, said the court should not interfere in government policy involving state immunity, which from Canada's standpoint is "the oil that allows for the smooth functioning of international relations."

"Canada has given priority to a foreign state's immunity over civil redress for citizens who have been tortured abroad," he wrote. "This policy choice is not a comment about the evils of torture, but rather an indication of what principles Parliament has chosen to promote given Canada's role and that of its government in the international community."

Justice Rosalie Abella, the lone dissenter, suggested the court had failed to uphold the integrity of international law, which prohibits torture. "The question then is how can torture be an official function for the purpose of immunity under international law when international law itself universally prohibits torture?"

Renu Mandhane, director of the International Human Rights Program at the University of Toronto's law school, which intervened in the case to argue for a right to sue torturers, said she feels deflated by the ruling. "There's something totally perverse that the State Immunity Act privileges the right of Iran to torture Canadian citizens over the right of Canadians to seek redress – and the court says that's okay.

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Iran participated in the court hearings, at the lower courts. The Supreme Court called the facts of the case "horrific," saying Ms. Kazemi was ordered detained in the very prison she had been photographing by Iran's chief prosecutor, Saeed Mortazavi.

She was then interrogated, beaten, tortured and sexually assaulted. She suffered a brain injury, a fractured nose, a crushed eardrum, strip-like wounds on her back and the back of her legs, fractured bones and broken nails on her hands and toes, and extensive trauma on and around her genital area, Justice LeBel wrote.