Prominent Iranian politicians and analysts are offering a gloomy assessment of upcoming nuclear talks with the United States and other world powers, insisting that Iran will not agree to any significant cuts to its nuclear program.

The elected officials and analysts — many of them close to Iran’s hard-line leadership — say it is highly unlikely that Iran would accept even a temporary halt in its production of enriched uranium, a key demand by Western countries during previous negotiations with the Islamic republic.

Some said recent economic sanctions and military threats have made Iranian leaders even more determined to continue enriching uranium, despite the worsening toll on Iran’s currency and oil industry.

“There will be no retreat whatsoever on our rights,” said Hossein Sheikholeslami, a former Iranian ambassador to Syria and once a leader of the student movement that took 52 U.S. Embassy workers hostage in 1979. “They impose unlawful sanctions on us, and now they want us to retreat. No way.”

It was not clear whether the assessments — made in interviews with a wide range of current and former politicians, diplomats and analysts — reflect the official view of Iranian leaders preparing to meet with negotiators from the United States, Russia, China, Britain, France and Germany. The six-country bloc agreed last month to an Iranian request to resume nuclear talks after a lull of 14 months.

Western officials also have played down expectations for the talks, which are not yet scheduled, although some suggested that the pessimism in Tehran could be a bargaining tactic. On Wednesday, Iranian officials dispatched a letter to the European Union reiterating the government’s desire for a diplomatic solution and asking that a date and a venue for the negotiations be set.

U.S. and European diplomats have been characterizing the talks as a modest first step that will mostly serve to demonstrate whether Iranian intentions are sincere.

“Maybe miracles happen,” a European diplomat said, insisting on anonymity in discussing his country’s position going into the talks, “but mostly we have to see if there is willingness by Iran to have a serious discussion of nuclear issues.”

Since agreeing to talks, Iranian leaders have publicly adopted a tough line on the subject of uranium enrichment. In a televised address last month, Iran’s supreme leader, Ayatollah Ali Khamenei, declared that possessing nuclear weapons was “a sin,” but he also vowed that Iran would not be forced to waive its legal right to a civilian nuclear energy program.

“Pressures, sanctions and assassinations will bear no fruit,” Khamenei said. “No obstacles can stop Iran’s nuclear work.”

The rhetoric adds to the predicament facing the Obama administration. In the past, the administration has backed compromises intended to effectively end Iran’s ability to convert uranium into weapons fuel while allowing Iran to save face by claiming that it reserves the right to enrich uranium for peaceful purposes. A compromise in 2009, for example, called on Iran to surrender nearly its entire stockpile of low-enriched uranium in exchange for nuclear fuel rods for Iran’s aging medical research reactor.

The White House has not yet staked out a position for the upcoming talks with Iran. Dennis Ross, who until last year was one of the administration’s top advisers on Iran, said any long-term deal with Iran would almost certainly need to include a suspension of uranium enrichment. But he also held out the possibility of short-term “confidence-building” measures that would effectively freeze Iran’s progress toward a nuclear-weapons capability.

One such measure, Ross said, might be an Iranian agreement to immediately halt production of a purer form of enriched uranium that can be quickly converted to weapons-grade. U.N. inspectors last month confirmed that Iran had recently tripled its production of “20 percent-enriched” uranium, a purer form of nuclear fuel than the 3.5 percent-enriched uranium generally used in nuclear power plants.

“One thing you try to do is stop the clock,” Ross said. “Getting a whole deal would be best, but if you can’t get the whole deal, you might at least get something that builds confidence and stops the clock.”

But even such interim measures can pose risks for a White House that is trying to delay a threatened Israeli military attack on Iran’s nuclear sites while fending off criticism from Republican presidential candidates who accuse the administration of being soft on Iran.

President Obama has sought to use a combination of diplomacy and economic and political pressure to force Iran to accept negotiated limits to its nuclear program. Obama has said he will never allow Iran to become a nuclear power, and he has left open the possibility of a military strike if other approaches fail.

On Thursday, European officials took a new step to isolate Iran economically, announcing that Iranian banks were being excluded from the international financial messaging network known as SWIFT. The Belgium-based electronic-payment system confirmed in a statement that Iranian institutions would be shut out of the system beginning Saturday.

The move adds to pressure from multiple rounds of sanctions and a European oil embargo set to begin in July. Iranian politicians have acknowledged the impact of the measures as Iranian companies are increasingly limited in what they can buy and sell on the international market. Yet, in the face of the collapse of Iran’s currency and increased fears of war, Iran’s top leaders have sought to rally the nation.

“We should not give in but resist sanctions and pressure by the enemies over the nuclear program,” President Mahmoud Ahmadinejad said during a meeting with visiting Zimbabwean Defense Minister Emmerson Mnangagwa. “We will not only prevail but eventually turn these pressures into new opportunities for further development and progress.”

Warrick reported from Washington.