More than 180 Iranian MPs have signed a letter praising former chief nuclear negotiator Ali Larijani, who has resigned from his post.
Mr Larijani had led talks on the nuclear programme with the West
A top foreign policy adviser to Iran's supreme leader also said Mr Larijani should not have been allowed to resign.
The BBC's Jon Leyne in Tehran says the resignation has revealed growing splits on how to proceed on the nuclear issue.
But Mr Larijani and his replacement, Saeed Jalili, said on Tuesday there was a consensus on nuclear policy in Iran.
"We will continue the nuclear discussions with strength. The nuclear issue is an issue on which there is a consensus of national harmony," Mr Jalili said in Rome where the two men met EU envoy Javier Solana.
"Iran's nuclear policies are stable and will not change," said Mr Larijani.
Western countries suspect Iran of trying to build nuclear weapons but Tehran says its programme is peaceful.
British Prime Minister Gordon Brown said he would seek to tighten sanctions aimed at discouraging Iran's nuclear programme.
"We will work through the United Nations to achieve this. We are prepared also to have tougher European sanctions," Mr Brown said after meeting Israeli Prime Minister Ehud Olmert in London.
"We want to make it clear that we do not support the nuclear ambitions of [Iran]," he said.
On Monday, 183 MPs signed a letter praising Mr Larijani's performance as a nuclear negotiator after he was replaced by Mr Jalili, the deputy foreign minister and a close ally of President Mahmoud Ahmadinejad.
Mr Larijani had repeatedly offered his resignation and, on Saturday, Mr Ahmadinejad finally accepted it.
The letter came as former foreign minister Ali Akbar Velayati - now senior foreign policy adviser to Supreme Leader Ayatollah Ali Khamenei - said the resignation had come at the wrong time.
"In the very important and sensitive situation where the nuclear issue is at the moment it would be better if this did not happen, or at least it was prevented," Mr Velayati said.
Although he was appointed by Mr Ahmadinejad, Mr Larijani reported directly to Ayatollah Khamenei, who usually has the final say on all state issues.
This is not an argument over whether Iran should have a nuclear programme, just how to get there, our correspondent says.
He says pragmatists believe in negotiating with the international community and talk of following the path of Japan, which has quietly gained a civilian nuclear programme that some observers believe could be quickly adapted to produce nuclear weapons.
By contrast, Mr Ahmadinajad seems almost to want a confrontation - it is not just that he wants the nuclear programme, he wants also to use it to challenge the West and by doing so to build up Iran's power, our correspondent adds.
Mr Jalili was meeting Mr Solana in Rome for the first time since taking over the position.
Mr Brown said Mr Solana would warn the Iranian negotiators about the risk of further sanctions during the Rome meeting.
Iran is working to enrich uranium on an industrial scale
The EU hopes to determine whether Mr Jalili's appointment signals a strengthening of Iran's stance on its nuclear programme.
But Mr Larijani accompanied his successor to the Rome talks, as the representative of Ayatollah Khamenei.
The deputy speaker of Iran's parliament has said that Mr Larijani resigned because he could no longer work with Mr Ahmadinejad, confirming suspicions that they had fallen out on policy, and possibly personality as well.
Iran is developing the technology to enrich uranium on an industrial scale. The enriched uranium can be used as fuel in a nuclear power station.
Some Western countries, led by the US, fear Iran will further process the enriched uranium for use in nuclear weapons.