Envoys from the US, EU and UN asked Iran to give an answer within two weeks or face possible new sanctions.

The meeting in Geneva on Saturday was the first time US and Iranian officials have held face-to-face talks about Iran's controversial nuclear programme.

"The Iranian people are steadfast," President Mahmoud Ahmadinejad said. <!-- E SF -->

They "will not retreat one iota in the face of oppressing powers," he said in the televised speech made to thousands of supporters in the southern town of Yasouj.

He also praised US participation in the Geneva talks, describing it as a "positive step forward" towards recognising Iran's right to acquire nuclear technology.

Iran says its nuclear programme is for entirely peaceful purposes, while the US and its allies believe it could be used to develop a nuclear weapon.

Interest

The BBC's Jon Leyne in Tehran says the speech contains the familiar language of defiance from President Ahmadinejad, but it the first time he has spoken out this strongly since the latest round of diplomacy gave some hope of a peaceful end to the crisis.

The revival of this tough language makes any sign of progress in the talks extremely unlikely, he adds.

Diplomats have been hoping that Iran would respond to a so-called "freeze-for-freeze" offer, under which a freeze of Iran's uranium enrichment programme at its current levels would be matched by a Western pledge not to strengthen sanctions on Tehran.

Our correspondent said Iran was interested in such an offer but it was unclear whether there were divisions in the leadership or whether the Iranians are playing for time.

Tehran's continued nuclear activity is defying UN Security Council demands to halt enrichment. <!-- E BO -->