Turkey denied Thursday a U.S. newspaper report claiming it had blown an Israeli spy ring working with Iranians on its soil to the authorities in Tehran, a sign of the strained ties between the once close allies.

Washington Post columnist David Ignatius said Prime Minister Recep Tayyip Erdogan's government had last year revealed to Iranian intelligence the identities of up to 10 Iranians who had been meeting in Turkey with Mossad handlers.

The world's positive response to the latest nuclear talks with Iran drew bitter skepticism 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.

Iranian analysts hailed Thursday the latest round of nuclear talks with world powers as a "new era" and a "new spring", praising Tehran's insistence on its right to enrich uranium.

There was no breakthrough at the two days of talks in Geneva, but most participants welcomed the positive atmosphere of the negotiations, the first since April.

The world must judge Iran's intentions by its actions and not by its "presentations" at the latest talks on its disputed nuclear program, a senior Israeli official said on Thursday.

"Iran will be judged by its actions and not by its presentations," the official said on condition of anonymity, in remarks just hours after world powers wrapped up two days of talks which the United States described as showing a new level of "seriousness".

Russia's chief negotiator on Iranian issues warned Wednesday there was "no reason to break into applause" after the latest round of talks on Tehran's disputed nuclear program concluded in Geneva.

"The results are better than what we had (in the previous round) in Almaty, but this does not guarantee further progress. There is no reason to break into applause," Russian news agencies quoted Deputy Foreign Minister Sergei Ryabkov as saying in the Swiss city.

Shimon Peres says Israel and its allies must retain a firm stance on Iran until it can show it does not threaten regional stability, despite its election of Hassan Rouhani as president.

In an interview published Monday by the Brazilian newspaper the Folha de Sao Paulo, the Israeli president poured cold water on Rouhani's recent charm offensive.

Iranian President Hassan Rouhani on Monday called for more freedoms in universities, where many professors and students have been sidelined over their political activities.

His remarks, carried by ISNA news agency, come a week after the moderate president urged Iranian police to be more lenient in enforcing rules on how women dress.

The Israeli intelligence minister called on the major powers on Monday to maintain pressure on Iran, saying that was what was driving it to seek a deal in nuclear talks.

Yuval Steinitz, who is also minister for international relations, was speaking on the eve of revived negotiations on Tehran's controversial nuclear program between Iranian officials and the P5+1 group of Britain, China, France, Russia and the United States, plus Germany.

U.S. Secretary of State John Kerry on Sunday said the window for diplomacy with Iran was "cracking open" following talks in London with EU foreign policy chief Catherine Ashton.

"Right now, the window for diplomacy is cracking open," Kerry told the American Israel Public Affairs Committee summit in Washington via satellite from London, ahead of next week's meeting between Iran and world powers.

Iran will not agree to ship out its stockpile of enriched uranium, one of its main negotiators said Sunday ahead of crunch talks with world powers on its nuclear program.

"We will negotiate about the volume, levels and the methods of enrichment but shipping out the (enriched) material is a red line for Iran," deputy Foreign Minister Abbas Araqchi told the state broadcaster.