Iran's president, Mahmoud Ahmadinejad, came under fire from domestic critics yesterday for his uncompromising stance on the nuclear issue as the US and Britain launched a new diplomatic effort to agree harsher UN sanctions they hope will force Tehran to halt uranium enrichment.
Mohammad Atrianfar, a respected political commentator, accused the president of using "the language of the bazaar" and said his comments had made it harder for Ali Larijani, the country's top nuclear negotiator, to reach a compromise with European diplomats.
The president made global headlines at the weekend by declaring that his country's quest for nuclear energy was an unstoppable train, adding to the sense of crisis as emergency talks got under way in London yesterday.
Critics from across the Iranian political spectrum took him to task for his "no brakes or reverse gear" remarks, bolstering claims in the west that his hardline position may be starting to backfire.
"This rhetoric is not suitable for a president and has no place in diplomatic circles," said Mr Atrianfar, a confidant of Hashemi Rafsanjani, an influential regime insider and rival of Mr Ahmadinejad. "It is the language people in the bazaar and alleyways use to address the simplest issues of life."
Fayaz Zahed, leader of the pro-reform Islamic Iran Solidarity party, criticised the president for seeking to emulate the populist Venezuelan president, Hugo Chavez, rather than internationally revered leaders such as Nelson Mandela or Vaclav Havel.
"The brake exists to get the train safely to its destination," Mr Zahed wrote in the newspaper Etemad-e Melli. "Perhaps on the journey, we might find the track broken and are obliged to move our passengers by using the reverse gear to get to a safer track. Iran is a nation of earthquakes, flood and national disasters! You are our head. We should be able to trust you."
Even the fundamentalist newspaper Resalat, usually a supporter of Mr Ahmadinejad, was critical. "Neither weakness nor inexperience and unnecessary rhetorical aggression is acceptable in our foreign policy," it said.
In London, the Foreign Office's political director, John Sawers, was talking to colleagues from the US, France, Russia, China - the other four permanent members of the UN security council - and Germany, holder of the EU's rotating presidency. The meeting was described as "a productive first session" by the Foreign Office.
The US and Britain are pushing for tougher financial and trade sanctions on Iran but will have to work hard to overcome objections from Russia and China before they can be codified into a new UN resolution.
The US representative, Nicholas Burns, the undersecretary of state, has been stressing Washington's commitment to diplomacy to resolve the crisis, in contrast to the continuing refusal of the White House to rule out military action.
Sergei Lavrov, the Russian foreign minister, underlined Moscow's unease when he criticised the US for talk of using force.
"Forecasts and suggestions about a strike on Iran have become more frequent and this is worrying," he was quoted as telling President Vladimir Putin.
A UN resolution in December barred the transfer of technology and know-how to Iran's nuclear and missile programme. New measures could include travel bans and asset freezes on individuals and organisations involved in them. Trade sanctions, including a ban on EU export credits, would be harder to agree.
The foreign secretary, Margaret Beckett, said Iran was treading a "dangerous route" but the west still wanted to negotiate. "The steps that we have taken are reversible. There is nothing that we would like better than to be able to reverse them and no longer to have to continue with sanctions," she said in Islamabad.