Iran warned Sunday that it would retaliate to any UN Security Council resolution ordering it to stop sensitive nuclear work.
"Any harsh measures will face a proportionate reaction," foreign ministry spokesman Hamid Reza Asefi told reporters.
"If the other side chooses anything but the path of negotiations, our attitude will change accordingly," he added, without elaborating on how Tehran could retaliate.
The warning came as a draft resolution was being circulated in the Security Council which would legally require Iran to suspend all uranium enrichment and reprocessing activities, at the centre of fears the country could acquire nuclear weapons.
Iran insists it only wants to enrich to make reactor fuel and argues that this is a right under the nuclear Non-Proliferation Treaty.
Several senior Iranian officials have already warned that the Islamic republic could end UN inspections and leave the NPT.
