Tehran made it clear that it would not approve the language of threats and reiterated that it would rather endure sanctions than back down on a programme it says is a matter of national pride.
Ahmadinejad was quoted by Iran's student news agency ISNA as saying on Sunday: "Iran has obtained the technology to produce nuclear fuel and Iran's move is like a train ... which has no brake and no reverse gear".
"We dismantled the rear gear and brakes of the train and threw them away sometime ago," Ahmadinejad was quoted as telling a gathering of Islamic clerics.
Another Iranian official affirmed Tehran's determination to press on with its nuclear programme, saying that the Islamic republic was ready for any possible scenario "even for war".
Manouchehr Mohammadi, one of the deputies to the foreign minister, was quoted by ISNA as saying at a conference in the central city of Isfahan:
"We have prepared ourselves for any situation, even for war."
Condoleezza Rice, the US secretary of state, said that what Iran needed was not a reverse gear, but a stop button.
She also pledged direct talks with Iranian officials if Tehran halts its nuclear enrichment programme.
The diplomatic stand-off has also been described as "dangerous" by foreign ministers from seven Muslim states who met in Pakistan on Sunday.
"It is vital that all issues must be resolved through diplomacy and there must be no resort to use of force," said a statement agreed by the ministers representing Pakistan, Egypt, Jordan, Saudi Arabia, Turkey, Indonesia and Malaysia.
New Zealand and Australia stepped into the controversy and urged Iran to be more transparent about its nuclear programme.
Hours prior to the London meeting, Alexander Downer, the Australian foreign minister, who is in the New Zealand capital, Wellington, for talks with counterpart Winston Peters, said Iran had failed to comply with the demands of the UN Security Council.
The concern of the international community is how to get Iran to cease its uranium enrichment programme and "cooperate fully in an open and transparent way with the International Atomic Energy Agency," Downer said.
"It is stubbornness and pride on Iran's part that has led to this impasse, and it can only lead to disaster for Iran"
Diom1982, Cork, Ireland
Send us your views
Helen Clark, the New Zealand Prime Minister, said: "The problem is the lack of transparency. What the international community is asking for is transparency, open your facilities, be honest, give the information, don't play games ... The pressure has to go on for full disclosure."
Iran is accused by the US of pursuing development of nuclear weapons.
Tehran denies the charges and says its nuclear programme is for peaceful means.