Iran's president has said that his country will not bend on its uranium enrichment programme, despite proposals by world powers aimed at bringing an end to Tehran's sensitive nuclear programme. 

"The Iranian people are steadfast and will not step back an inch against the oppressive powers," Mahmoud Ahmadinejad said on Wednesday at a rally in the southwestern province of Kohgelouyeh-Boyerahmad.

His comments come after world powers said Iran has a fortnight to respond to an offer which seeks to end the five-year crisis over Tehran's nuclear ambitions.

Gordon Johndroe, the US national security spokesman, said: "We hope the Iranians will provide a positive answer," to incentives offered by a number of countries for Iran to halt its sensitive nuclear fuel work.

"[But] if they do not, the international community is united that more sanctions are coming," he said.

Britain, China, France, Russia and the US – the five permanent UN Security Council members - plus Germany have offered to help Iran pursue a civilian nuclear programme in return for suspending enrichment.

They want Tehran to refrain from installing more uranium-enriching centrifuges in exchange for a block on further sanctions - the so-called freeze-for-freeze approach.

Sanctions threat

Iran is already facing three sets of UN Security Council sanctions for continuing its nuclear work, which the West says is aimed at making nuclear weapons.

But Iran denies that it is looking to produce a nuclear bomb and says its programme is aimed at producing electricity.

Ahmadinejad said the US presence in the Geneva talks was a "positive step" but he said that Iran would not change course, despite the threat of further sanctions.

"The Iranian nation does not value your threats. You are mistaken if you think you can force this nation to back down with sanctions, threats and pressure," Ahmadinejad said.

He advised US officials "not to ruin your positive step with irrelevant comments and a colonialist language".

Ahmadinejad’s latest statement comes after the US sent William Burns, an under-secretary of state, as its envoy to negotiations between Saeed Jalili, Iran's chief negotiator, and EU officials in Geneva last week.