Iranian and U.S. negotiators meet Tuesday for a new round of talks over a nuclear program that Iranian leaders are vowing to keep despite a threat from the U.S. Senate of harsh sanctions should the talks fail.
The Obama administration has said the negotiations in Vienna will lead to a pact that would curtail Iran's ability to convert nuclear fuel to atomic weapons fuel. Israel, which sees the program as a threat to its existence, has threatened to attack Iran's nuclear facilities if negotiations do not prevent Iran from being able to build a bomb.
Though Iran agreed to limit some of its technology in an initial agreement in November it has since said it will not roll back centrifuges that can enrich uranium into bomb material, nor will it abandon a plutonium plant project in Arak or open up for full inspection a secret plant in Fordow.
The hard stands come as a majority in the U.S. Senate is unified behind a bill that would impose harsh sanctions on Iran if it fails to curtail its program.
"At the end of this process, will Iran's supreme leader be able to wake up one day, kick out inspectors and race to the bomb? 'No' should be the only acceptable answer to that question," said Sen. Mark Kirk, a Republican from Illinois.
Kirk says any pact must have a clear goal of ending the nuclear program that is in violation of United Nations resolutions calling for Iran to suspend all nuclear enrichment. President Obama is trying to prevent the bill from coming to a vote, saying it would anger the Iranians into walking away from negotiations.
Jofi Joseph, former director for non-proliferation for the White House National Security Council, says the United States must pursue negotiations to determine how much Iran is willing to concede with its nuclear program.
"We simply do not know today where Iran's ultimate bottom lines rest," said Joseph.
The U.S. chief negotiator with Iran, Wendy Sherman, has said that if Iran's nuclear program is for peaceful purposes as it claims then it "does not need" a fortified underground enrichment facility like it has in Fordow or a heavy-water reactor at Arak.
The reactor under construction in Arak could produce enough plutonium every year for two bombs, and once it goes online a strike against it could result in a significant radiation explosion.
Also in dispute are Iran's 19,000 centrifuges, about half of which are enriching uranium. The West has been unable to inspect all sites where it suspects nuclear material may be produced, so it cannot verify what Iran has.
Israel says Iran is less than six months from having enough material to make a bomb.
Iran's military is experimenting with longer range ballistic missiles and is suspected of working on nuclear detonators at a secret facility in Parchin.
Senior Iranian officials have said they will give up nothing, however.
Iran's chief negotiator, Mohammad Javad Zarif, referred to Sherman's testimony as "worthless."
"Iran's nuclear technology is non-negotiable and comments about Iran's nuclear facilities are worthless and there is no need to negotiate or hold talks about them," Zarif said, according to official Iranian media.
Ali Akbar Salehi, who heads Iran's nuclear program, appeared to offer a concession last week when he said the Arak plant could be changed into a light-water facility that would produce less plutonium and "allay the worries" of the West. But a few days later the spokesman for Iran's delegation to the United Nations, Hamid Babaei, said that will not happen.
Meanwhile, Salehi announced last week that Iran has a new generation of centrifuges "15 times more powerful than the previous generation," according to Iran's state broadcaster IRI Broadcasting. Iran also announced last week it successfully tested a new ballistic missile and laser-guided projectile, according to official news agency IRNA.
The interim agreement reached with Iran Nov. 24 by negotiators from the USA, United Kingdom, France, Russia, China and Germany also gave Iran at least $7 billion in relief from existing economic sanctions. In return, Iran agreed to limit some of its activity.
But Iranian officials said publicly in Iran after the agreement that any limits it agreed to could be reversed in a matter of days.
Abe Sofaer, a former State Department legal adviser on Iran and author of Taking On Iran, dismissed such talk as "bravura statements" intended for domestic audiences.
The many Iranian statements about their negotiating position are a sure sign the talks will be difficult, if not fruitless, says Reuel Marc Gerecht, an analyst at the Foundation for Defense of Democracies who used to focus on Iran as a CIA officer.
When Zarif and others say in the most clear-cut way they are not going to dismantle that program, "they're not kidding," Gerecht says. "They're intent on finishing the centerpiece of what's been their military strategy for 20 years."
Talking is "worth a try," Gerecht said. "Because you're only other options are surrender or military strikes, (neither of which) are not that appealing to the White House."