The ceasefire agreement for Syria came into force Monday evening and, if it holds, could lead to Russia and the US coordinating strikes against jihadist targets.
But the details of the agreement, including the regions in which the coordinated military action could take place, have not been made public.
Russia has also called for disclosure of such details, with a foreign ministry spokeswoman saying Thursday that Moscow had called for the terms to be released to avoid "any misinterpretations".
The coordination of Russia-US military action can only take place if Moscow and the Assad regime fully meet commitments to cease violence for seven days, according to the agreement.
Meanwhile the US has committed to trying to get moderate rebel groups to separate from radical jihadist fighters on ground.
France is a member of a US-led coalition that has been bombing so-called Islamic State jihadists and Ayrault said full disclosure of the deal would help "us better understand what was negotiated in order to ensure its effectiveness."
Ayrault said that the United Nations General Assembly in New York would be an opportunity to discuss the situation.
He also expressed concern that groups belonging to the moderate opposition fighting the regime could be targeted in areas where jihadists are operating.
"We need to differentiate the groups, know them and not take the risk of striking the ranks of the moderate opposition," Ayrault said.
- with AFP