MOSCOW — High-level nuclear talks between Iran and six world powers fizzled Tuesday, creating increased opportunity for Israel to use the setback to argue military force is the only way to stop Tehran from developing atomic arms.

As she announced the indefinite pause in negotiations, European Union foreign policy chief Catherine Ashton said they could be resumed — but only if a low-level July 3 meeting of technical experts in Istanbul finds enough common ground to warrant such a step.

Officials from Western nations involved in the talks acknowledged huge differences between the two sides but insisted the diplomatic track had not been derailed. But the lack of progress in Moscow is sure to be seen by critics as a sign that talks are ineffective at persuading Tehran to curb uranium enrichment, a process that can make both reactor fuel and the core of nuclear warheads.

Strong comments by Foreign Minister Laurent Fabius of France, one of the countries at the table in Moscow, reflected Western frustration. He spoke of "the large gap between the two sides," and warned that "sanctions will continue to be toughened" to pressure Tehran into a nuclear compromise.

Iran says it is not interested in nuclear weapons. But Israel says Iran is stretching out the talks to move closer to the ability to make them, and it has threatened to attack the Islamic Republic as a last resort. Israel may argue that the negotiations are turning into "talks about talks" — something the U.S. and its allies have vowed they will not tolerate.

Ahead of the inconclusive last round of talks in Baghdad on May 23, Prime Minister Benjamin Netanyahu accused Tehran of playing a "chess game" with the international community, declaring he sees "no evidence whatsoever that Iran is serious about ending its nuclear program."

Netanyahu did not present any ultimatums then, but Israeli officials have repeatedly said time is running out to avoid military action as a last resort to prevent Tehran from developing nuclear arms. It's a scenario with potential to draw the U.S. into a war between the Jewish state and Iran.

Even if Israel does not strike, the talks' indefinite suspension could spell trouble for U.S. President Barack Obama by giving Mitt Romney, his presumptive Republican rival in this year's race for the presidency, a wider platform for criticizing him for his alleged weak response to international concerns about Tehran's nuclear aims.

But Ashton, who convened the talks between Iran and the six powers — the United States, Russia, China, Britain, France and Germany — defended the decision to kick contacts down to a lower level.

She said it was "the right way to go forward" and suggested Iran's actions would determine if negotiations between top officials resume.

"We expect Iran to decide whether it is willing to make diplomacy work, to focus on reaching agreement on concrete confidence-building steps, and to address the concerns of the international community," Ashton said in a statement.

The six want Tehran to stop enriching uranium to a level that is just steps away from its use as the core of nuclear warheads.

But Iran says it is enriching only to make reactor fuel or medical isotopes and insists it has a right to enrich under international law. With neither side ready to accept what the other brought to the table in the form of inducements to compromise, diplomats familiar with the negotiations said they were in trouble from day one.

Reflecting the differences, top Iranian negotiator Saeed Jalili said Tuesday it was up to the six to "get out of the past deadlocked path and take steps in the path of cooperation."

Along with recognition of the right to enrich, Iran seeks relief from growing U.N. and other sanctions, including spreading international embargoes on its oil sales. That is something the six are ready to grant only if Tehran agrees to enrichment suspension and related measures and Jalili, in comments to reporters, warned of an unspecified "appropriate response" if sanctions were not eased.

Ashton, speaking separately to reporters, said that after the technical experts report back from the Istanbul meeting, senior officials from both sides will discuss the results. Then, she said, she and Jalili will determine if there is enough common ground to resume the high-level talks.

The deadlock remained although both Obama and Russian President Vladimir Putin jointly urged Iran to show flexibility at the Moscow talks ahead of Tuesday's session.

"We agree that Iran must undertake serious efforts aimed at restoring international confidence in the exclusively peaceful nature of its nuclear program," they said on the sidelines of the meeting of G-20 nations in Mexico.

In addition to longer-term U.N. and other sanctions, Tehran is now being squeezed by the widening international embargo on its oil sales, which make up more than 90 percent of its foreign currency earnings.

Sanctions levied by the U.S. have already cut exports of Iranian crude from about 2.5 million barrels a day last year to between 1.2 million and 1.8 million barrels now, according to estimates by U.S. officials. An EU embargo on Iranian crude that starts July 1 will tighten the squeeze.

The six nations formally are only prepared to ease restrictions on airplane parts for Iran's outmoded, mostly U.S.-produced civilian fleet and are offering technical help with aspects of Iran's nuclear program that cannot be used for military purposes.

While not budging on lifting existing sanctions or those already decided upon, diplomats familiar with the talks told The Associated Press that the six are also prepared to guarantee that no new U.N. penalties will be enacted if Tehran compromises enough. The diplomats demanded anonymity because that possible offer has not yet been formally made.

The six also want Fordo, the underground Iranian facility where most of the higher-level enrichment is taking place, shut down and for Iran to ship out its higher-grade stockpile. Fordo is of special concern because it might be impervious to air attacks — a possible last-resort response to any Iranian bomb in the making.