Speaking at a conference in Paris on Tuesday, the government official said Tehran would recommence mining uranium and enriching it.
Iran is also to build a heavy-water reactor which can produce plutonium, Muhammad Saidi, vice president of the Atomic Energy Organisation of Iran (AEOI), said.
"The people and government of Iran are determined to open their way through the tortuous path of peaceful use of nuclear technology despite all imposed restrictions and difficulties," he said.
Saidi told a conference on nuclear power that Iran, one of the world's major oil producers, still needed nuclear energy "to reverse the trend of unrestrained use of fossil resources".
The US charges that Iran is using its civilian nuclear energy programme as a cover for secretly developing nuclear weapons. Iran has consistently denied the allegation.
"The people and government of Iran are determined to open their way through the tortuous path of peaceful use of nuclear technology despite all imposed restrictions and difficulties"
Iran has asked the European Union and Russia to respect its right to enrich uranium, an activity the EU is trying to convince Iran to give up to ensure it is not producing nuclear weapons.
Britain, France and Germany have been negotiating for the EU with Iran since December to secure "objective guarantees" that the government will not use its atomic energy programme to acquire nuclear weapons.
Iran insists it does not even consider abandoning enrichment to be on the table in the talks, despite its having temporarily suspended enrichment as a confidence-building measure.
A new round of negotiations is due to start in Paris on Wednesday. A steering committee has to evaluate work done since December and decide how negotiations can go on.