The world's positive response to the latest nuclear talks with Iran drew bitter scepticism from Israel, which warned its Western allies Thursday they risked being duped into easing sanctions prematurely.

Energy Minister Silvan Shalom, a former foreign minister, went further, accusing the European Union and the United States of being more interested in the resumption of Iranian oil exports than with addressing an issue that Israel regards as a threat to its very existence.

Washington, which has had no diplomatic relations with Tehran since the aftermath of the 1979 Islamic revolution, said Iranian negotiators had shown a greater level of "seriousness and substance" in this week's talks than ever before.

But Israel, which has mounted a massive lobbying campaign to keep up the economic and military pressure on its number-one foe, insisted Iran's intentions could be proved only by concrete steps to wind down its nuclear programme, not by "sweet talk" from its new president.

"Iran will be judged by its actions and not by its presentations," a senior Israeli official said.

"Until significant steps are carried out on the ground which prove that Iran is breaking up its military nuclear programme, the international community must continue to impose sanctions upon it," he added.

"The pressure of sanctions brought Iran to this point and must continue until Iran is stripped of its nuclear military programme."

After the talks in Geneva on Tuesday and Wednesday, Iranian officials touted a "breakthrough" in the decade-old negotiations on allaying international concerns over its nuclear ambitions.

They said they were hopeful of a "new phase" in Iran's relations with the world after outlining a three-step plan, including spot checks on nuclear facilities, to try to reach a comprehensive agreement "within a year."

Although there was no official response from the office of Prime Minister Benjamin Netanyahu, Israel's army radio quoted a source close to him as taking a hard line.

"The Americans are the angels while the Iranians have given nothing," the source said, adding that there was "no reason for any enthusiasm."

Writing in Israel's Maariv newspaper, Iran specialist Emily Landau said she saw no policy changes of substance from President Hassan Rouhani, the moderate cleric who took office in August and on whom the West has pinned its hopes of a breakthrough.

"Except for the more relaxed tones and the demonstratively positive approach, there is nothing significant of substance this time that we didn't have in the previous rounds in 2012 and earlier this year," wrote Landau, an analyst at Israel's Institute for National Security Studies.

"As long as there is no indication that Iran has changed direction in its nuclear plans and has decided to give up its intent to develop a military nuclear capability, all of its proposals should be seen as tactical steps in the negotiations with the international community."

Israel's energy minister said the international community's drive to end Iran's long isolation on the nuclear issue was primarily motivated by a concern to reduce world oil prices, driven higher by the Western sanctions on Iran's exports.

"Diplomacy of 2013 is based, first and foremost, on the economy," Shalom told public radio.

"The world is currently going through a financial crisis and ... the Iran issue needs to be resolved to broaden supply and bring prices down. All the rest is just empty words."

But Eldad Pardo, senior researcher on Iran at the Hebrew University of Jerusalem, said Iranian oil was reaching international buyers anyway.

"The US does not need Iranian oil, and Iranian oil goes out anyway through China and those countries who need it," he told AFP.

Israel, which has the Middle East's sole if undeclared nuclear arsenal, has repeatedly threatened to take unilateral action if necessary to keep Iran from developing the capability to build a bomb of its own.

Netanyahu renewed the threat before parliament on Tuesday in his latest salvo against the historic overtures between Tehran and Washington.