At a meeting with Iran's chief nuclear negotiator in Geneva on Saturday, six world powers gave Iran two weeks to answer calls to rein in its nuclear activities, which they suspect may be aimed at producing atom bombs, or face tougher sanctions.

"The Iranian nation ... will not retreat one iota in the face of oppressing powers," Ahmadinejad said in a speech broadcast live on state television.

Iran says its nuclear programme is a peaceful drive to generate electricity so that the Islamic Republic, the world's fourth-largest crude producer, can export more of its oil and gas.

"The Iranian nation has chosen its path," Ahmadinejad said.

Addressing the major powers which have offered economic and other incentives in return for Tehran halting its most sensitive atomic work, he said:

"If you come forward based on law, justice and logic, the Iranian nation will negotiate on important global issues and will cooperate in solving the problems of humanity."

Iran has repeatedly ruled out suspending uranium enrichment, as the powers say it must do before formal negotiations on their offer can start. Enriched uranium can provide fuel for power plants but also material for weapons if greatly refined.