Mohammad Reza Bahonar was quoted by the official IRNA news agency on Thursday as saying Iran "doesn't accept" the offer, drummed up at a nuclear meeting in Vienna.
Following three-day talks in the Austrian capital, Iran said it would decide on the plan on shipping its uranium to Russia for enrichment.
The international community sees this as a way to curb Tehran's ability to build a nuclear weapon. Iran says its nuclear program is for peaceful purposes only.
Bahonar's remark is the first reaction on the draft in Tehran. But he does not speak for the government, which is to decide on the matter.
