JUDY WOODRUFF: The deadline for reaching an interim deal with Iran over its nuclear program is in the final hours, and there are new doubts about whether an agreement will be reached in time.

A U.S. State Department spokeswoman indicated there's only a 50/50 chance of it happening by tomorrow, as gaps remain between Iran and other parties at the talks in Switzerland.

Indira Lakshmanan has been covering the twist and turns at the talks for Bloomberg News. I spoke to her a short time ago.

And Indira Lakshmanan joins us now.

Indira, literally down to the wire, just a day left. How does it look?

INDIRA LAKSHMANAN, Bloomberg: Absolutely.

We have got 24 hours left. And the only question that matters at this point, to which none of us have the answer, is, are they have going to a deal or no deal? And it seems as if the ministers themselves don't know.

We saw the Russian foreign minister, Sergei Lavrov, actually left talks today after less than a day, said that's it, he's done, he's going back to Moscow, and he's only going to come back tomorrow if he has a sense that they're really ready to sign a deal.

And we had the Chinese foreign minister sounding a more optimistic note, talking about progress. And John Kerry himself also said there was some progress, but there are some tricky issues that still need to be resolved. So, 24 hours from now, we will know whether they were able to put something together that they could call a framework accord or whether they're going to have to go back to the drawing board and extend this deadline one more time.

JUDY WOODRUFF: Do you have a good sense at this point, Indira, of what the sticking points really are?

INDIRA LAKSHMANAN: Yes, for the most part, it seems as if Iran is most upset about the pace of sanctions relief.

Remember that what Iran is going to get in return for the willingness to restrict its nuclear program and have invasive inspections is to be lifted out from underneath these economic and banking and oil sanctions that have hit its economy so hard over the last five years.

So it wants sanctions relief immediately and it wants it permanently, especially from U.N. sanctions as well. And the international community has said, no way, that that is going to be a phased sanctions release, and they're not going to be lifted. They're only going to be suspended, so they can be put back. That's one thing.

Research and development is another question. And what happens to Iran's program after year 10? Because they're thinking about a 10-year deal. So, what happens between years 11 and 15 to make sure that Iran doesn't suddenly at that point break out with its nuclear program and go back into big development?

JUDY WOODRUFF: So, have they — is it felt that they have agreed on how much enrichment of uranium the Iranians should be allowed to do?

INDIRA LAKSHMANAN: You know, the way that it's been described to us repeatedly, and I think this is pretty apt, is that it's like a Rubik's Cube. Every piece has to fit together.

So you can have agreement on one thing and think that you're done with that. And that was the case with the stockpiles of enriched uranium, which we thought were going to be shipped out by Iran to a third country, probably Russia. Iran said last night, no, we never agreed to that. And the State Department said today, that's right, they had not yet agreed to that. So it seems like each piece has to come into place.

But we think that there is more agreement on centrifuges, there's more agreement on the Arak heavy water reactor to stop it from producing plutonium. But these other issues, like sanctions and research and development, are really big. And so, if you sort of limit one thing then you can allow a little more in another area. So that's why it matters. Every piece fits together like a puzzle.

JUDY WOODRUFF: So, Indira, you call ate framework accord. If they do reach agreement, what would it look like? Is it a piece of paper, a joint declaration?

INDIRA LAKSHMANAN: Yes, that's the $60,000 question.

The United States would like to have a few pages long of bullet points that really lays out what Iran is going to do, so they can take that document to Congress and to the American people and say, this is what we got agreement on.

We have heard that Iran says, no, either we have to have a much longer document, which is really not possible to get, or something very brief, more like a declaration. I think, either way, whatever happens, you're still going to see three more months of really intense haggling over every if, and, or but, every line of this agreement, is what we have been told by U.S. officials, until the June 30 deadline for having the final accord.

JUDY WOODRUFF: And that would be — that would be — there would still be more work to be done after this.

INDIRA LAKSHMANAN: Absolutely.

JUDY WOODRUFF: Indira Lakshmanan, I know you will be watching. Thank you, Bloomberg News. We appreciate it.

INDIRA LAKSHMANAN: Thanks.