"We have said clearly that any phrase in a resolution aimed at transforming the voluntary pledge by Iran to suspend uranium enrichment into a legal obligation will be unacceptable to us," the secretary of Iran's Supreme National Security Council, Hassan Rowhani, was quoted as saying by the official news agency IRNA.
The comment came the day before the Vienna-based UN nuclear watchdog is due to meet to discuss Iran's nuclear programme, amid US allegations that the clerical regime's bid to generate atomic energy is merely a cover for nuclear weapons development.
Iran last month agreed to meet a raft of IAEA demands including the suspension of uranium enrichment, but insists its pledge to suspend its controversial work on the sensitive nuclear fuel cycle is voluntary and temporary and could be reversed at any time.
The country also gave to the IAEA what it said was a full declaration on its nuclear activities, in which it owned up to a series of violations of the nuclear Non-Proliferation Treaty (NPT).
Iran also pledged to sign and implement an additional protocol to the NPT which would allow the UN inspectors to carry out tougher checks on its highly secretive nuclear work.
But halting uranium enrichment is seen by diplomats as central to preventing Iran from ever acquiring nuclear weapons, and Britain, France and Germany -- whose foreign ministers secured Iranian concessions when they converged on Tehran last month -- are pressing for Iran to totally stop enrichment in return for guarantees of the supply of nuclear fuel for Iranian reactors from overseas.
The problem here, however, is that legitimate work on the nuclear fuel cycle is permitted under the NPT, even though states that master the cycle can be within just months of acquiring material for nuclear warheads.
Maintaining assertions that Iran's domestic production of nuclear fuel is perfectly legitimate, Rowhani asserted that it was under no obligation to concede to demands that go beyond the NPT or additional protocol.
"We have said that after all this, our relationship with the agency should be normalised and we will not accept anything beyond the additional protocol and the safeguard clauses," he was quoted as saying.
Iran says its mastering of the nuclear fuel cycle is crucial for the independence of its atomic energy programme, tagged as crucial for meeting future energy needs and reducing its dependence on its massive oil and gas reserves.
The Islamic regime also vigorously denies it has any intention to acquire nuclear weapons.