Defense Minister Moshe Ya'alon urged his American counterpart Chuck Hagel not to ease up sanctions on Iran in a meeting between the two on Tuesday.
"Any relief in sanctions will lead to the collapse of the sanctions regime," he said, warning that easing the economic pressure on Tehran will allow it to continue enriching weapons-grade uranium.
"We must not fall into the trap of easing up on sanctions as a trust-building measure before the Iranians meet the demands set to them," he said.
The US secretary of defense assured Ya'alon that the United States will be "clear-eyed" and committed to ensuring that Iran does not develop nuclear weapons while Washington pursues diplomacy, AFP quoted Pentagon spokesman George Little as saying.
The US "will not waver from our firm policy to prevent Iran from obtaining nuclear weapons," Little said.
Ya'alon and Hagel met six days before negotiations over Iran's nuclear program resume in Geneva on October 15.
Iran has lost no opportunity under new President Hassan Rouhani to reiterate that it has only peaceful nuclear aims and to call for an end to sanctions on its oil and banking industries, which have caused a precipitous currency devaluation and cut oil export revenue by billions of dollars.
Negotiators from the six nations - the five permanent members of the UN Security Council and Germany - have in the past asked Iran to address their most pressing concern, the enrichment of uranium to 20 percent fissile purity, as an initial step towards building confidence after decades of mistrust.
In return they had offered relief from sanctions on trade in gold and petrochemicals, a proposal Iran rejected as too weak.
The lead US negotiator, Wendy Sherman, held out the possibility last week of giving Iran some short-term sanctions relief in return for concrete steps to slow uranium enrichment.
There was no more detail, and she did say fundamental sanctions - which Iran considers to be those targeting its banking and oil sectors - will remain in place until all of Washington's concerns have been addressed.
Reuters contributed to this report.
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