LONDON - The West should not push Iran too far in talks over the Islamic republic's nuclear ambitions because failing to get a deal could bolster hardliners in Tehran, a former British foreign minister warned on Friday.

But Jack Straw told the BBC he was "optimistic," on returning to London from Iran where he led a British delegation including former finance minister Norman Lamont, Conservative member of parliament Ben Wallace and Labour lawmaker Jeremy Corbyn.

In an interim deal reached in Geneva on November 24, Iran agreed with world powers to freeze some of its nuclear program as the first step towards a long-term deal that many hope could resolve a dispute over its nuclear ambitions.

The election of Hassan Rouhani as president in June has raised hopes in Western capitals a breakthrough can be made, though Supreme Leader Ayatollah Ali Khamenei said on Thursday negotiations had revealed US enmity towards Iran.

Straw, British foreign minister from 2001 to 2006 under former Prime Minister Tony Blair, said pushing Rouhani too far could endanger a possible deal while allowing hardliners to gain the upper hand in Tehran.

He said the West should be sensible in the negotiations between Iran and the group of countries known as the P5+1, the five permanent members of the UN Security Council - the United States, Russia, China, Britain and France - plus Germany.

"It requires skilful management by Dr. Rouhani, particularly over the nuclear dossier, but it also requires sensible decisions by the West at the so-called P5 plus 1 negotiations, so they don't push the Iranians too far," Straw said.

"If they push the Iranians too far, the Iranians, the decent people, won't be able to make a deal and we we will end up back where we started with another Ahamdinejad figure."

Mahmoud Ahmadinejad courted international controversy during his 2005-2013 presidency with uncompromising rhetoric against the West and Israel.

Iran is under UN, US and European Union sanctions for refusing to agree to UN Security Council demands that it halt all enrichment- and plutonium-related work.

Tehran rejects Western allegations that it is seeking the capability to produce nuclear weapons, saying its nuclear ambitions are purely civilian.

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