Secretary of State John Kerry sits with Iranian Foreign Minister Javad Zarif in New York in September. (Stan Honda/AFP/Getty Images)

International negotiations over Iran's nuclear program kick off in Geneva on Tuesday, and, despite all the high hopes for a breakthrough, there's already a bad sign. Deputy Foreign Minister Abbas Araghchi said that Iran would not allow its stockpiles of enriched uranium to be removed from the country. "The shipping of materials out of the country is our red line," he said.

This is a bad sign for three reasons. First, Iran had actually agreed, in 2010, to a nuclear deal that would have required it to ship much of its enriched uranium abroad, in exchange for finished fuel rods. The idea was that Iran could scale down its uranium enrichment but still have a nuclear program. The deal, brokered by Turkey and Brazil, fell apart, but the point is that Iran now says it won't accept something that it previously said it would accept.

That gets to the second reason this is bad: Iran seems to be stepping away from a compromise, at a moment when everyone expects it to take steps toward compromise. Its position is hardening, not softening. For nuclear negotiations to work, both Iran and the West will have to compromise a bit, to take steps closer to each other's positions. Tehran just did the opposite of that. And Araghchi's language was awfully categorical.

The third reason this is bad is that any final nuclear deal would almost certainly include a limit on how much enriched uranium Iran is allowed to possess. The contours of a deal have been clear for years -- it's the process of getting everyone to agree that's always been the challenge -- and a major provision of that deal is for Iran to accept that it can only have so much enriched uranium. That means giving some enriched uranium up. The fact that Iran now says it won't do that puts us further from a deal.

The big caveat, though, is that Iran might just be negotiating here. A nuclear deal looks more possible now than it has been in years, maybe ever. Deal-making has just gone from theoretical to actual, which means that everyone's incentives have just changed. A year ago, Tehran's strategy, if it wanted to get to a nuclear deal, was to make tantalizing offers to get everyone to the negotiating table. Now that we're at the table, their incentive to take the toughest stance possible is so that they have more room to negotiate, more stuff to give up. This is absolutely true of the United States as well; we're also shifting negotiating strategies in this way.

Still, Araghchi's use of the phrase "red line" is worrying. It's a very categorical way to describe Iran's position and will make it tough for Tehran to back off this demand, if indeed it is just a negotiating ploy. Given that one of the biggest challenges for a deal will be overcoming Iranian hard-liners who oppose the very idea of a compromise, that maybe just got even harder; the hard-liners can always point to Araghchi's "red line" to argue against giving up enriched uranium.

In the grand scheme of things, this is not a major moment; history books will probably not remember it as a turning point, one way or the other, in the long-running Iranian nuclear crisis. But it is a bad sign ahead of the Geneva talks, and a reminder after three months of promising signs and feel-good messages, that the United States and Iran still have a very long and difficult path to a nuclear deal.