Iran proclaimed advances in nuclear know-how, including new centrifuges able to enrich uranium much faster, a move that may heighten its confrontation with the West over suspicions it is seeking the means to make atomic bombs.
Tehran's determination to pursue a nuclear programme showed no sign of wavering despite Western sanctions that are inflicting increasing damage on its oil-based economy.
"The era of bullying nations has passed. The arrogant powers cannot monopolise nuclear technology. They tried to prevent us by issuing sanctions and resolutions but failed," President Mahmoud Ahmadinejad said in a television broadcast on Wednesday.
"Our nuclear path will continue."
But Iran's Arabic-language Al Alam television said the government had handed a letter to EU foreign policy chief Catherine Ashton expressing readiness to "hold new talks over its nuclear programme in a constructive way".
An Ashton spokeswoman confirmed receipt of the letter, saying she was evaluating it and would consult the United States, Russia, China and other partners among the big powers.
Iran has long refused to negotiate curbs on its nuclear programme, saying it is intended purely for civilian uses, including producing electricity for booming domestic demand.
The United States and Israel have not ruled out military action against Iran if diplomacy and sanctions fail.
Washington played down Iran's announcement, saying the advances were neither new nor very impressive. "We frankly don't see a lot new here. This is not big news. In fact it seems to have been hyped," a State Department spokeswoman said.