French-Iranian academic Fariba Adelkhah's research focuses on political and social anthropology. (File photo: AFP)

Iran has sentenced French-Iranian academic Fariba Adelkhah to six years in prison on national security charges, her lawyer reported on Saturday, drawing protests from the French government, which demanded her immediate release.

Branch 15 of Tehran's Revolutionary Court sentenced her to five years jail for gathering and conspiring against Iran's national security. She was also sentenced to a one-year jail term for propaganda against the Islamic Republic.

"The court has sentenced her to six years," said Saeid Dehghan, her lawer, adding he would appeal against the sentence

France's foreign ministry said Adelkhah's conviction was politically motivated.

"This sentencing is not based on any serious element or fact and is thus a political decision," the ministry said in a statement. "We are urging Iranian authorities to immediately release Mrs Adelkhah."

Iran has rejected France's previous calls to release the 60-year-old anthropologist who has been detained since June 2019, saying the demands were an interference in Tehran's internal affairs. Tehran does not recognize dual nationality.

Spying charges against Adelkhah had been dropped, Dehghan said in March, but she remained in jail on other security-related charges.

In March, Iran released Adelkhah's partner, French academic Roland Marchal, who was detained along with her. Marchal was released after France freed Iranian engineer Jalal Ruhollahnejad, who was detained over alleged violations of U.S. sanctions against Tehran.

A French court in May 2019 approved the extradition of Ruhollahnejad to the United States to face charges of attempting to illegally import U.S. technology for military purposes on behalf of an Iranian company U.S. officials said was linked to Iran's elite Revolutionary Guards.

The powerful Guards have arrested dozens of dual nationals in recent years, mostly on espionage charges.