France on Friday said it had summoned the Iranian ambassador to protest the imprisonment by Iran of two prominent French academics for half a year, saying their detention was "intolerable" and expressing grave concern one was now on hunger strike. The imprisonment of Fariba Adelkhah and Roland Marchal has added to tensions between Tehran and Paris at a time when President Emmanuel Macron is seeking to play a leading role in defusing tensions in the standoff on the Iranian nuclear program. The envoy "was reminded of France's demand that Fariba Adelkhah and Roland Marchal are released without delay and that the Iranian authorities show total transparency over their situation," the foreign ministry said in a statement. "As the President (Macron) and Foreign Minister (Jean-Yves Le Drian) have said on several occasions, their imprisonment is intolerable," it added. Adelkhah and Marchal, both academics at Sciences Po in Paris, have been held by the Iranian authorities since June. The university and supporters said this week that Adelkhah and another detained academic, Australian Kylie Moore-Gilbert, had started an indefinite hunger strike just ahead of Christmas. The French statement said the ministry had made clear to the ambassador "our grave concern over the situation of Mrs. Fariba Adelkhah, who has stopped taking food". It also said the ministry reaffirmed France's demand of allowing consular access, a request which has so far been refused. Iran does not recognize dual nationality. "The French authorities will continue to act with determination to obtain their release," it added. A specialist in Shiite Islam and a research director at the university, Adelkhah was arrested on charges of "espionage" that have been rubbished by her supporters. Marchal had come to Iran to visit Adelkhah and stands accused of "collusion against national security", according to his lawyer and supporters fear he too will soon be formally charged. Iranian media said earlier this month their bid to be released on bail was rejected and their case will now go before the Revolutionary Court which handles high-profile cases in Iran. Melbourne University academic Moore-Gilbert's detention on charges of "spying for another country" was confirmed in September, but her family said at the time that she had been detained for months before that. In an open letter, Moore-Gilbert and Adelkhah, who are sharing a cell at the notorious Evin prison in Tehran, said they had started the hunger strike on Dec. 24 the name of "academic freedom". Noting that Moore-Gilbert had now been held for over 15 months and Adelkhah for over 7 months, they said: "We have been subjected to psychological torture and numerous violations of our basic human rights." The letter was published by the US-based Center for Human Rights in Iran (CHRI), which said it was sent the letter by a source with contacts inside the prison and that the two women were held in Evin's Ward 2-A, controlled by the Revolutionary Guards. The latest tensions come after Xiyue Wang, an American scholar who had been serving 10 years on espionage charges, was released by Iran earlier this month in exchange for Massoud Soleimani, an Iranian who had been held in the US for allegedly breaching sanctions. Iran has said it is open to more such prisoner swaps with the United States. Tehran is still holding several other foreign nationals in high profile c