U.S. President Joe Biden has few real diplomatic alternatives to trying to persuade Iran to resume compliance with the 2015 nuclear deal and all appear harder to achieve, current and former U.S. and European officials said.

Indirect U.S.-Iranian talks on reviving the deal have been on hold since the last round ended on June 20 and Iran has made clear it is not ready to resume before Iranian President-elect Ebrahim Raisi takes over in August.

The hiatus, which U.S. and European officials attribute to the hard-line cleric's election, has raised questions about next steps if the talks hit a dead end. The U.S. State Department has acknowledged it may need to rethink its stance.

The problem is that experts agree there are few options to the 2015 deal under which Tehran limited its nuclear program to make it harder to acquire nuclear weapons - an ambition it denies - in return for relief from economic sanctions.

"I think all the alternatives are worse for us. I think they are worse for Iran. And frankly, I think, at the end of the day, Iran will suffer - I don't know if they suffer more than we will - but they will be in a bad situation," a senior U.S. official told Reuters on condition of anonymity.

"Which is why we have argued now for some time that the best option is a strict return to compliance with the (deal). That’s our analysis," the U.S. official said.

Washington would do all it could to revive the deal, the official said, but added, "we have to be prepared to live with the alternatives."

When former U.S. President Donald Trump abandoned the agreement, named the Joint Comprehensive Plan of Action (JCPOA), he reimposed U.S. sanctions that largely deprived Tehran of its ability to export oil and have caused economic misery in Iran.

'MORE FOR MORE, LESS FOR LESS'

One alternative to the JCPOA, which former U.S. and European officials called "more for more," would entail Iran accepting greater limits on its nuclear and perhaps other activities in return for greater sanctions relief.

It will likely be harder to negotiate such a broader deal than to restore the 2015 accord, whose parameters are at least defined, even if they may need tweaking to reflect Iran's expanded nuclear work since Trump violated the agreement.

A version of "more-for-more" would limit the negotiation to the tradeoffs between restricting Iran's nuclear program and easing economic sanctions.

A wider and thornier version would entail Iran also curbing its ballistic missile program and support for regional proxies, red lines Iranian officials say they will not cross.

A second alternative, sometimes called less-for-less, might require fewer limitations to Iran's nuclear program in return for less sanctions relief.

This might be the worst of both worlds for Biden, however, since he could be criticized for giving Iran economic benefits and getting fewer nuclear limits in return.

"An agreement weaker than the 2015 one would be politically unsustainable in the U.S.," said Gerard Araud, France's former ambassador to the United States.

"I don't see an alternative to the JCPOA other than 'maximum pressure' but this regime has shown its resilience and I don't see it caving to it," he added.

He was referring to Trump's policy of increasing economic pressure in the hopes Iran would capitulate.

Tehran, for its part, has raised pressure on Washington by starting the process to make enriched uranium metal and by talk of enriching uranium to 90 percent, or weapons grade - both steps that could help it make nuclear arms.

A senior diplomat involved in the talks said it was vital to convince Raisi's team that hopes they can negotiate fewer nuclear limits for more sanctions relief, the equivalent of "less for more," were misplaced.

"They may think time is on their side," he said on condition of anonymity. If that's the case, he said, "they are mistaken."

Former U.S. government Middle East specialist Dennis Ross said Tehran was likely to keep pushing Washington by expanding its nuclear program.

"When they decide the administration has reached the limits of what it (will) concede, I suspect you will see a deal reconstituting the JCPOA," Ross said.