Iran's government was forced to deny Tuesday it had already struck a nuclear deal with the West, after a lawmaker accused its negotiators of secretly selling the country short.

In a sign of the domestic political tension surrounding talks being held abroad with world powers, Iran's foreign ministry threatened to prosecute the member of parliament who said an agreement that breaches the Islamic republic's "red lines" had been settled.

A group of hardline MPs in Tehran have repeatedly warned Iran has already given up too much in talks with the United States and other leading nations under an interim deal that traded curbs on its nuclear programme for limited sanctions relief.

However Iran's President Hassan Rouhani and Foreign Minister Mohammad Javad Zarif have pushed ahead despite pressure back home, consistently stating that a comprehensive agreement is possible by a November 24 deadline.

The West wants to close all avenues to Tehran developing an atomic bomb, by cutting back its nuclear enrichment program, shutting down suspect facilities and imposing tough international inspections.

In return, world powers would suspend and then gradually lift crippling economic sanctions imposed on the Islamic republic.

Iran denies seeking atomic weapons but insists on having "industrial level enrichment" for its civilian energy programme. It wants all sanctions lifted and no restrictions on its existing nuclear technology.

Tuesday's remarks, however, by conservative lawmaker Alireza Makani laid bare the resistance Rouhani faces.

"According to received information and news, an agreement between the Iranian delegation and the American side has been finalised," Makani said, according to the Iranian parliament's website.

"There are reports that the system's red lines have been crossed in an implicit agreement which will no doubt weaken the rights of the nation and trample upon all our nuclear achievements," it quoted him as saying.

- Ayatollah's 'red lines' -

The so-called red lines refer to 11 points set by Iran's supreme leader Ayatollah Ali Khamenei which must be observed by negotiators, led by Zarif, before the Islamic republic will sign a deal.

One of the stipulations includes "the absolute need for Iran's uranium enrichment capacity to be 190,000 SWU (Separate Work Units)" -- close to 20 times its current processing ability. The West has said this is the main stumbling block to agreement.

"MPs are completely kept in the dark," Makani said. "If the negotiating team acts without considering the parliament it will cause many problems which would be against the national interest... then the negotiating team should bear the consequences."

Makani did not provide proof for his allegations, which were met by a stern rebuke from the foreign ministry.

"The nuclear negotiating team is aware of the system's red lines and is careful and sensitive to adhere to them," ministry spokeswoman Marzieh Afkham was quoted as saying by the official IRNA news agency.

"The only agreement reached was regarding the title of the final agreement, the 'Joint Comprehensive Action Plan,'" she said.

"Such remarks... are slander against the negotiating team and (those making them) can be prosecuted," Afkham added.

"The negotiating team knows clearly and more than anyone that any agreement that does not consider the system's red lines is worthless."

- 'Forest of distrust' -

US Under Secretary of State Wendy Sherman has spoken of "a forest of distrust" between the West and Iran.

But in months of discussions since the interim agreement struck last November took effect in January, some progress has been made.

This includes possible changes in the design of an unfinished reactor at Arak so that it produces less weapons-grade plutonium, enhanced UN inspections, and alterations to Iran's fortified Fordo facility.

However, Makani's comments were indicative of Sherman's scepticism.

"The silence of our diplomatic apparatus regarding the excessive demands of the American negotiators has caused the Great Satan (the United States) to be presumptuous... and to speak in a hallucinatory manner and repeat its nonsense," Makani said.

He also hit out at a campaign led by Iranian filmmakers, apparently with the foreign ministry's backing, that has said there is "no deal that would be worse than no deal at all".

"We consider this to be a disgrace," the MP added. "We call on Iran's security apparatus to reveal what is behind this campaign."