The Iranian president said today Iran will move forward with uranium enrichment despite international demands to stop, adding that Iran's nuclear programme is like a train without brakes.
Mahmoud Ahmadinejad also repeated his call for negotiations, saying the time for "bullying" had expired.
"The train of the Iranian nation is without brakes and a rear gear," a radio station quoted Mr Ahmadinejad as telling a gathering of Islamic clerics.
Iranian President Mahmoud Ahmadinejad
"We dismantled the rear gear and brakes of the train and threw them away sometime ago."
His comments come a day before senior officials of the five permanent members of the UN Security Council - Britain, the US, France, China and Russia - and Germany were set to meet for an emergency summit in London to discuss measures against Tehran over its defiant nuclear stance.
The International Atomic Energy Agency last week reported that Iran had ignored a UN Security Council ultimatum to freeze its uranium enrichment programme and instead had expanded the programme by setting up hundreds of centrifuges.
In December, the Security Council imposed limited sanctions on Iran over its refusal to suspend enrichment and gave it a 60-day grace period to halt enrichment. That grace period expired on Wednesday.
Iran has repeatedly refused to halt enrichment as a precondition to negotiations about its programme. Enriched to a low level, uranium is used to produce nuclear fuel but further enrichment makes it suitable for use in building an atomic bomb.
The United States and several of its allies fear that Iran is using its nuclear programme to produce atomic weapons - charges Iran denies, saying its aim is to generate electricity.
Mr Ahmadinejad also said Western countries feel threatened by Iran's nuclear developments because they feel their own powers are diminishing. "The Westerners are not concerned about the existence and activity of ... centrifuges in Iran; they are concerned about the collapse of their hegemony and hollow power," the radio station quoted him as saying.
Earlier today, deputy Iranian foreign minister said Tehran was ready for any scenario in its nuclear row with the West. "We have prepared ourselves for any situation, even for war," Manouchehr Mohammadi, one of the deputies to the foreign minister, was quoted by Iran's student news agency ISNA as saying at a conference in the central city of Isfahan.
"If they issue a second resolution, Iran will not respond and will continue its nuclear activities," he said.