Iran said its hotly awaited proposal to break the deadlock with world powers over its nuclear drive was well received Tuesday, in fresh talks seen as a key test for new President Hassan Rouhani.

The hour-long PowerPoint presentation by Foreign Minister Mohammad Javad Zarif and his team was for the first time delivered in English, Western officials said, underlining a new mood in the often-tense nuclear discussions.

Senior Iranian negotiator Abbas Araqchi praised the "very positive environment" and said the "reaction was good" across the table.

He told reporters in Geneva that all sides had agreed not to reveal details, but insisted the proposal was "very comprehensive" and eclipsed one made in April under Rouhani's predecessor that ended up a dead letter.

But Iranian state news agency IRNA quoted him as saying that snap inspections of the Islamic republic's nuclear facilities were not on the table.

"It does not exist in the offer," Araqchi told IRNA.

Iran has drawn other red lines, saying it will not accept any demand to suspend uranium enrichment or ship out stockpiles of purified material.

Iran's two-day meeting in Geneva with the European Union-chaired P5+1 group -- the United States, Britain, France, China and Russia, plus Germany -- ends a six-month freeze sparked by its refusal to curb uranium enrichment in exchange for the easing of punishing international sanctions.

"The climate of the meeting was very good and very constructive. The proposal that we have introduced has the capacity to make a breakthrough," Araqchi said after Tuesday's opening session.

The talks are the first since Rouhani took office in August after conservative Mahmoud Ahmadinejad wrapped up his second four-year term in power.

Rouhani, who is seen as more moderate, has pledged transparency on the nuclear programme and engagement with the international community to help lift the sanctions.

"That's part of a broader project I think by President Rouhani for Iran in an unstable region... to rebuild the Iranian economy from the mess it's in, and to end Iran's isolation from the international community," Malcolm Chalmers, of the London-based think tank the Royal United Services Institute for Defence and Security Studies, told AFP.

Western powers and Israel suspect Iran of developing an atomic bomb, a claim vehemently denied by Tehran which insists its nuclear programme is for peaceful purposes.

'We are not here to waste our time'

"We are very serious. We are not here symbolically, to waste our time. We are serious for target-oriented negotiations," said Araqchi.

But Iran's archfoe Israel has warned the world not to fall for "sweet talk" from Rouhani.

Western negotiators insist they are not naive but that the change in Tehran's tone, at least, is clear.

EU spokesman Michael Mann underlined the "very different" atmosphere.

"We have come here with a sense of cautious optimism and a great sense of determination because we believe it's really time now for tangible results," Mann told reporters in Geneva.

"There are signals from Tehran that they want to engage in these negotiations, that they want to be more transparent. The proof would be if they made real progress," he said.

"We are on our side ambitious to move forward quickly... The ball remains in their court."

Earlier, Zarif said Tehran's plan contained three steps that could settle the long-running nuclear standoff "within a year", with the first achievable "within a month or two, or even less".

Acknowledging that "accumulated mistrust" made resolving the standoff difficult, he said he hoped the Geneva meeting would at least yield a roadmap for higher-level talks.

A senior US administration official said earlier in Geneva that any easing of sanctions would be "targeted, proportional to what Iran puts on the table".

"We are hopeful, but that has to be tested with concrete, verifiable actions," the official said.

A first meeting between Zarif and his counterparts from the six powers took place last month during the UN General Assembly, accompanied by a landmark two-way meeting with US Secretary of State John Kerry.

Israel -- believed to be the Middle East's only nuclear armed state -- warned Tuesday against accepting "cosmetic concessions" that would not impede Iran's weapons quest.

Kerry underlined Sunday that while the diplomatic window was "cracking open", Washington was serious about never allowing room for a nuclear-armed Iran.