GWEN IFILL: The efforts to reach an Iran nuclear deal appeared so close today that Iran's president even tweeted about it, calling it a good beginning. But in no time at all, that tweet was deleted and reports of new negotiating snags surfaced.

So, the sun set again in Vienna today with no agreement.

Indira Lakshmanan is covering the talks for Bloomberg News, and she joins us now.

Indira, late this afternoon, we heard there was the announcement overnight. Then there wouldn't be an announcement overnight. This keeps going on. I wonder what the latest that you know about why.

INDIRA LAKSHMANAN, Bloomberg: Yes, it's deja vu all over again, Gwen.

And if it's been a roller coaster for the past 17 days, we're now going into day 18, and this has been the most extreme roller coaster in the last 24 hours. We thought we were going to have a deal. Then Foreign Minister Zarif came out on his balcony, sort of Evita Peron style. We all yelled up him and said, will there be a deal?

He made a motion with his head, and indicated, no, there would not be. We're now after midnight in Vienna, so the negotiators have blown past their fourth deadline in the last 18 days, but the latest reports we're getting, our sources are telling us from four different delegations that it's very, very likely that there will be an announcement of a final deal in the early hours of the morning.

So we're talking about possibly as early as pre-dawn Vienna time, which might be as early as before midnight Washington time.

GWEN IFILL: Boy, that's the latest possible thing. But what is it that they're trying to smooth out? What are these last-minute hangups which people keep referring to?

INDIRA LAKSHMANAN: Right.

Well, I reported 24 hours ago that that arms embargo issue actually had been mostly smoothed out, and the issue is that, on the U.N. side, the Iranians wanted the arms embargo lifted right away. Now it looks like it will be a phased process over the next two to eight years for lifting that embargo.

But what they have been arguing about all day today is language because language matters, and we have lawyers from seven different countries going over literally every comma and every T that's crossed and I that is dotted in 100 pages of documents. So, again, we're talking about a 100-page-long document with five technical annexes that is meant to last for a long time.

Some elements of this deal will last 10 years, others for 15, and yet others for 25. So the U.S. and Iran, in particular, are really concerned that they want to get this exactly right. No one wants to have to go back.

You can't reopen it and renegotiate it, so it's really about getting the language right the first time. And one thing I want to remind you when we were here a couple of months ago from Lausanne, Switzerland, having a similar conversation after midnight, you will remember that when they actually released the deal last time, the framework agreement, the United States had one set of talking points and Iran had a different set of talking points.

GWEN IFILL: I remember that.

INDIRA LAKSHMANAN: And that really caused some problems in the last couple of months when they have been trying to negotiate.

So what we understand from both the United States and the Iranians this time is, there's going to be one comprehensive statement that speaks for both sides. Imagine how hard that is, Gwen, to do that, because both the Americans and the Iranians are trying to show their home audiences that they won. So how do you come up with language that says you won in Tehran and also says you won in Washington when they're both facing hard-line audiences at home?

So, I think a lot of it has been about words.

GWEN IFILL: You mentioned that they have now blown through four deadlines. Do deadlines matter at all anymore?

INDIRA LAKSHMANAN: Well, you know, the deadlines mattered insofar as the Obama administration has said the deadlines are a forcing mechanism. They force people to sit down and actually make a decision. Apparently, in this case, they didn't force them to do that much.

But I think, as John Kerry said, this can't go on forever. They can't stay at the negotiating table forever. Iran has sort of very cleverly taken that and turned it on its head by saying, hey, we face no deadlines, we will stay here as long as it takes, and if anyone leaves the negotiations, it's their fault, not ours.

That of course puts the United States on the spot because if negotiations were to collapse, Iran could easily say, well, that's America's fault, they walked out, we didn't walk out.

So we have had all of the parties really trying to keep both the United States and Iran at the table. A funny moment earlier today was when Sergei Lavrov, the Russian foreign minister, walked into a meeting with Zarif, the Iranian foreign minister, who said, how are you, Mr. Lavrov, and he said angry.

He was smiling at the time, but I'm sure there was more than a little truth to that, because the Russians, the Europeans, the Chinese, they are frustrated. They want the deal to be done. They feel like they have already signed off on it, and they wish that the Americans and the Iranians would get their houses in order, get the wording straight, so everyone can move on, go home after 18 days of this and really two-and-a-half years.

GWEN IFILL: Well, Indira, I know that sleep is overrated and you're going to be up again late tonight waiting on this last shoe to drop. Thank you so much for joining us.