"In practice, the answer has almost been given and it is negative. That is a shame, a shame, a shame," Kouchner told the Israeli daily Yediot Aharonot ahead of a visit to the region later this week.
The comments came as both the United States and Russia expressed frustration at Iran's failure to give an answer three weeks after it received the offer in high-level talks to defuse the stand-off.
The West suspects Tehran is trying to develop a nuclear weapon under cover of its civilian nuclear energy programme. Iran vehemently denies the claims.
Kouchner said so far attempts to reach a deal with Iran had not gone well. "None of those meetings were particularly successful. We are waiting. It isn't good, and it is very dangerous," he told the paper.
