Iran and six world powers resumed nuclear talks Monday no closer to progress than in previous rounds, and with the clock ticking on international diplomatic efforts to persuade Tehran to curb activities that could be used to make atomic weapons.

Diplomats from several nations meeting with Iran in Moscow describe the talks as crucial. They say it will likely be the last in a series and that, if negotiators fail to make headway in persuading Tehran to stop higher-grade uranium enrichment, it’s unclear if or when new talks would occur.

While Iran wants the other side to recognize its right to enrich and blink first by easing sanctions, the six powers say the onus is on Tehran to show it is ready to compromise. Such a stalemate makes the chances of substantial progress unlikely in Moscow.

In an interview with CNN published on Monday, President Shimon Peres said the Iranians have not stopped their nuclear program and warned that "it may lead to war."

Commenting on what he expects from the Moscow talks, Peres said, "I am not sure that something will happen there for two reasons. Firstly, the Iranians think this is just a warning, that people are not serious enough. And secondly, they believe they can introduce a split in the coalition that President Obama has built. I don’t think it will happen because the danger is uniting, not the policy. Iran is a real danger."
 
Asked if he believed a military threat is credible in Iran's view, the president said, "If the Iranians will understand seriously that this is an option, maybe we shall not need it."

He stressed, however, that "If they think this is a bluff, then it may lead to a war."

"For that reason, the warning must must be credible, the sanctions must be credible. So let’s first of all use the non-military means, indicating to the Iranians, ‘gentlemen, better you agree with a non-military confrontation than look for other options,'" Peres said.
 
He also noted that time was running out for the international community because the Iranians "continue to build the bomb."

Peres's comments echo warnings by the United States and its Western allies that time is running out for a diplomatic solution to the standoff. But this time such warnings carry more weight than before both for Iran and its negotiating partners — the U.S., Russia, China, Britain, France and Germany.

Iran would be most immediately hurt by a lack of progress in Moscow followed by a long hiatus in new negotiations.

In addition to longer-term U.N. and other sanctions, Tehran is now being squeezed by a widening international embargo on its oil sales, which make up more than 90 percent of its foreign currency earnings. It desperately needs those sanctions lifted, but the six say it needs to make the first move on cutting back on uranium enrichment.

The White House also stands to lose.

Failed talks at Moscow with no immediate prospect of new meetings would almost certainly expose President Barack Obama to criticism of weakness in dealing with Iran from Republican presidential candidate Mitt Romney — and from Israel, which has threatened to attack the Islamic Republic’s nuclear installations should diplomacy fail.

It is unclear if the Jewish state would actually make good on such a threat and, if so, when. But any military move would likely draw in the U.S., widen the conflict through much of the Mideast and further hobble countries already in economic tailspin by driving oil prices sky-high.

All that should be avoidable, considering that each side is keenly interested in what the other has to offer.

Western nations in particular are eager for Iran to stop enriching uranium at a level just a few steps from weapons-grade material.

Western nations also want Fordo, the underground Iranian facility where most of this enrichment is taking place, shut down and 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.

Iran, in turn, wants sanctions lifted, particularly those eroding its oil sales.

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

Iran denies it is hurting from the oil penalties, but in India last week, U.S. Secretary of State Hillary Clinton said the sanctions are “sending a decisive message to Iran’s leaders.”

“Until they take concrete actions to satisfy the concerns of the international community, they will continue to face increasing isolation and pressure,” she said.

Like canny chess players unwilling to expose their king, both sides have been waiting for the other to make the first move. But too long a wait could translate into opportunity missed.

“Having accumulated precious assets that bolstered their hand in negotiations, both parties are now loath to use the leverage they sacrificed so much to acquire,” the Brussels-based International Crisis Group said of the standoff.

Repeating Iran’s mantra, Ayatollah Ahmad Jannati, a senior Iranian cleric, said curbing uranium enrichment was not on the table.

“The Iranian nation has withstood years of Western pressure and sanctions for the realization of its nuclear energy rights and it will not give them up now,” Iranian state TV quoted him as saying during Friday prayers in Tehran.

Others are more conciliatory, reflecting the many and ever-changing voices of Iran on the nuclear issue.

The talks are being convened by EU foreign policy chief Catherine Ashton, and diplomats say Iranian chief nuclear negotiator Saeed Jalili told her Monday that Iran was ready to discuss enrichment in Moscow. On Saturday, Iranian President Mahmoud Ahmadinejad told the German daily Frankfurter Allgemeine that his country is ready for “a positive step if the other side also takes steps.”

But the problem of who takes the first step remains — along with whether that will be big enough to be followed by others.

The six came to Moscow 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 the six are also prepared to guarantee that no new U.N. penalties will be enacted if Tehran shows enough compromise. The diplomats demanded anonymity because that possible offer has not yet been formally made.

Washington has warned Tehran of the alternatives should it not be willing to meet the six powers’ demands.

“The window for diplomacy is not indefinite,” a senior U.S. administration official told AP. “There is tremendous international unity and (oil) sanctions will continue to ratchet up come the beginning of July when our bilateral ones and the EU’s come into full force.

“So, these, too, can serve to affect Iran’s calculus and make them willing to finally meet its international obligations. The onus is on Iran to take concrete steps or it will face mounting pressure and isolation.”

But the proposals from the six that already are on the table fall short of what Iran says it seeks, at least publicly — a move to ease pressure now by easing existing or looming sanctions.

“Temporary suspension of 20% enrichment in return for plane spare parts is like swapping gold for chocolate. It’s a joke,” said Esmaiel Kowsari, a member of the Iranian parliament’s National Security and Foreign Policy Commission who often speaks on the nuclear issue.

“Effectively, the West wants Iran to surrender in Moscow. That will never happen.”

Ahead of the next round of talks, U.S. officials and experts interviewed by The New York Times on Saturday offered their take on what the nuclear talks would bring.

"The reality is that [the Iranians are] on the verge of a choice between having a nuclear program or an economy,” said Cliff Kupchan, a senior analyst on the Middle East at the Eurasia Group, a consulting firm. “There’s nothing like no money in your wallet to straighten your senses.”

However, Kupchan and other analysts expressed skepticism over any breakthroughs in the Moscow talks. They say even if the Iranians show they are prepared to accept an interim agreement, the U.S. and the other world powers are likely not yet willing to accept Tehran's terms.

The powers are unlikely to accept a delay in sanctions, and Obama does not appear likely to recognize Iran's right to enrich uranium, as granting that concession to the Iranians would set the U.S. president up for criticism from Romney and the Republicans in an election year, The New York Times said.

In addition to timing, what distinguishes Monday's talks is the location, as it is the first of three sessions to be held in one of the P5+1 negotiating countries, Russia. The talks also come at a time when Russia, at odds with the international community over its ties with Syrian President Bashar Assad's government, "could use a diplomatic victory," The New York Times reported.

Even though Russia and the U.S. have clashed over Syria, the two countries are closely aligned when it comes to their position on Iran, according to officials quoted by The New York Times.

“The Russians have made it very clear that they expect the Iranians to advance the discussion in Moscow — not to just come, listen and leave,” Clinton said last week. “We’ll know once it happens. But I think that the unity and the resolve that has been shown thus far is of real significance.”

Meanwhile, in the backdrop of the Moscow talks, Iran announced this week that it arrested some 20 suspects for alleged links to assassinations of Iranian nuclear experts that Tehran claims is part of covert operations led by Israel.

Sunday's remark by Iranian Intelligence Minister Heidar Moslehi is the first official number on the detentions. Last week, Iran announced it had made arrests linked to the slayings.

Moslehi claims the suspects moved between Iran and Israel through a neighboring country. He did not name the country, but Iran has accused Azerbaijan of harboring terrorists linked to Israel.

At least five Iranian nuclear experts have been killed since 2010. The U.S. and Britain have denied any roles, but Israel has remained silent on Iran's accusations. In May, Iran hanged a man convicted in the killing of a nuclear physicist in early 2010.

The arrested suspects are accused of killing Iranian nuclear scientists Majid Shahriari in November 2010 and Mostafa Ahmadi-Roshan in January, as well as Reza Qashqai, Roshan's bodyguard.