PARIS, Feb 2 (Reuters) -

French Foreign Minister Jean-Yves Le Drian has urged Iran to free two French nationals held in prison since last June, who he said were both unwell.

Roland Marchal is a senior researcher at the Sciences Po university in Paris and Fariba Adelkhah, a Franco-Iranian dual national, is also an academic there.

Authorities have dropped spying charges against Adelkhah but are still holding her on other security-related charges, her lawyer said on Jan. 7. He said Marshal was being held on suspicion of acting against Iranian national security.

"We consider these detentions intolerable. We have made this known to the highest authorities, including President (Hassan) Rouhani," Le Drian said in a joint interview with the broadcasters LCI and RTL and the newspaper Le Figaro.

"We know that they are not in a very good condition and that they are not always being treated well ... We think Iran would give a strong signal by releasing them."

The French newspaper Le Figaro reported in January, citing a colleague of the academics, that Adelkhah had been on hunger strike since Dec. 24 and was in extremely poor health, while Marchal was "very unstable".

The academics' university association says Marchal, an Africa expert, was arrested at Tehran airport as he arrived to spend the Eid religious holiday with Adelkhah in Iran.