"I confirm here that we will maintain the sanctions as long as we are not certain that Iran has definitively and irreversibly renounced its military programme to obtain nuclear weapons," he said.
His remarks were made in an address to the Israeli parliament just two days before the start of a fresh round of talks in Geneva aimed at rolling back Tehran's nuclear programme in exchange for sanctions relief.
"France will not let Iran arm itself with nuclear weapons," he said to widespread applause.
Israel and the West have long accused Iran of seeking a nuclear weapons capability, allegations denied by Tehran, which insists its controversial uranium enrichment programme is for entirely peaceful purposes.
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"Everything must be done to resolve this crisis," he told the Knesset, saying the P5+1 group of world powers had made "credible and solid proposals" in its negotiations with Iran in Geneva.
"Now it is up to Iran to respond, not just with words nor with vague promises - no. By concrete and verifiable steps."
"I'm concerned, gravely concerned, that this deal will go through and in one stroke of the pen, it will reduce the sanctions on Iran -- sanctions that took years to put in place -- and in return for this, Iran gives practically nothing," Israeli Prime Minister Benjamin Netanyahu said at a joint news conference with Hollande on Sunday.