Iran has called its uranium enrichment work "irreversible", days before a UN deadline for the programme to stop.
Iran claims it has struck a deal to enrich uranium with Russia
Foreign Ministry spokesman Hamid Reza Asefi also said demands for Iran to suspend its nuclear research work were "not on the agenda".
The UN Security Council called on Iran to suspend enrichment by 28 April, amid fears it wants to make nuclear weapons.
Iran - which insists its programme is peaceful - announced this month it had enriched uranium for the first time.
The UN Security Council, in a statement issued on 29 March, asked nuclear watchdog the International Atomic Energy Agency (IAEA) to report back within 30 days on whether Iran has complied with the UN call.
But Mr Asefi told a weekly news conference: "Iran's uranium enrichment and nuclear research and development activities are irreversible".
NUCLEAR FUEL CYCLE
Mined uranium ore is purified and reconstituted into solid form known as yellowcake
Yellowcake is converted into a gas by heating it to about 64C (147F)
Gas is fed through centrifuges, where its isotopes separate and process is repeated until uranium is enriched
Low-level enriched uranium is used for nuclear fuel
Highly enriched uranium can be used in nuclear weapons
He said that so long as the IAEA report contained "expert assessment", there would be "nothing left to worry about".
"However, if the report comes out and somehow puts pressure on Iran or speaks with a language of threats, naturally Iran will not abandon its rights and it is prepared for all possible situations and has planned for it."
The BBC's Tehran correspondent, Frances Harrison, says there has been a flurry of diplomatic activity by Iran in the run-up to the deadline, and some calls internally for a less confrontational approach towards the West on the nuclear issue
Mr Asefi said Iran was still discussing with Russia a plan for Iran to enrich uranium on Russian soil.
Iran first gave details of the plan in February, and on Saturday, state radio said an outline agreement had been reached, but details were still to be worked out.
Our correspondent says that the problem with the plan, which has been seen as a possible solution to the stand-off with the West, is that Iranian officials continue to adamantly rule out halting enrichment research on their own soil.
Iran's announcement that it had enriched uranium for the first time has thrown attention on to its enrichment technology.
President Mahmoud Ahmadinejad said earlier this month that Iran was testing a more advanced centrifuge, known as a P-2.
The P-2 centrifuge can enrich uranium more quickly, raising fears in some Western capitals that Iran could develop nuclear weapons more quickly than originally thought.
Mr Asefi said Iran had not yet used P-2 centrifuges in its enrichment work.
"So far, we have never used P-2 centrifuges, and what we have used is P-1 machines. We have informed the agency (IAEA) about that.
"No-one can deny Iran from using these devices. However, they have not yet been used," said Mr Asefi.
Iran says its nuclear programme is for purely peaceful purposes
Mr Asefi also said there were no plans for Iran to meet the US to discuss the situation in war-torn Iraq.
"Nothing has been scheduled and set. Preparations have not even been made for these talks," Mr Asefi told reporters.
US Secretary of State Condoleezza Rice had authorised the US ambassador to Iraq, Zalmay Khalilzad, to reach out to the Iranians for direct talks on Iraq, raising hopes that the two sides might also been drawn into discussions on the nuclear stand-off.
"We are not in hurry because we have been pessimistic about US intentions as we still are. It is nothing important," said Mr Asefi.